Mechanical Design Data and Machine-Element Reference: Cylindrical Roller Bearings (Single Row)

Cylindrical Roller Bearings (Single Row)

• Bore diameter ranges covered: 30–55 mm
• Key parameters listed for each bearing designation:
  • Principal dimensions: bore diameter (d), outer diameter (D), width (B)
  • Basic load ratings: dynamic (C) and static (C₀) — measured in Newtons (N)
  • Fatigue load limit (Pᵤ) — threshold below which fatigue life is theoretically infinite
  • Speed ratings: reference speed for grease and oil lubrication (r/min)
  • Mass — in kilograms
  • Bearing dimensions: inner ring (d₁, d₂), outer ring (D₁), fillet radii (r₁₂ min, r₃₄ min), and abutment dimensions (dₐ min, Dₐ max, rₐ max)
• Bearing type designations include NU, NJ, NUP, and N series — each denoting a specific internal configuration of rollers and flanges
• Angle rings are listed separately with their own designation codes, masses, and dimensions (B₁, B₂)

Spherical Roller Bearings (Single Row)

• Bore diameter ranges covered: 20–55 mm
• Available bore types: cylindrical bore, tapered bore (designated with "K" suffix)
• Designation codes: CC, E, EK — indicating different internal designs and load capacities
• Key parameters are the same as cylindrical roller bearings plus additional calculation factors:
  • e — a limiting value for the ratio of axial to radial load
  • Y₁, Y₂ — axial load factors used in equivalent dynamic load calculations
  • Y₀ — static axial load factor
• Abutment and fillet dimensions include: dₐ (min), Dₐ (max), rₐ (max), plus additional dimensions for shoulder diameters and chamfer limits
• A footnote indicates that permissible axial displacement from the normal position of one bearing ring relative to the other is specified in manufacturer catalogues

Journal (Plain) Bearings

Definition and Construction

• A journal bearing (also called a bush or plain bearing) consists of a bearing surface surrounding a rotating shaft (the journal), housed within a stationary housing
• The journal is not necessarily larger in diameter than the shaft — it is often the same diameter
• Two main types of journal bearings:
  • Pressure-lubricated type — lubricant is pumped into the bearing under pressure (e.g., automotive engine bearings); requires complex design and is outside the scope of standard data manuals
  • Non-pressure-lubricated type — relies on self-lubrication or simple oil/grease supply; suitable for off-the-shelf selection
• Flange-type bearings have a flange on one side to accommodate thrust loads in addition to radial loads

Bearing Materials

• Journal material: typically a hard material with a fine, smooth, ground or lapped finish
• Bearing material: a dissimilar, softer material with a relatively open and porous finish
• Why dissimilar materials are required:
  • Prevents localised welding and seizure
  • Soft material allows embeddability of foreign particles
  • Porous, open finish retains lubricant
• Common bearing materials:
  • Metallic: bronze (copper-tin alloy), white-metal alloys (lead-tin-aluminium-antimony-copper), cast iron (historically used, now rare)
  • Non-metallic: nylon, phenolics, PTFE (polytetrafluoroethylene)
• Common lubricants: oils and greases; some special bearings use water or even air (dry operation)

Porous Bronze Bearings

• Manufactured using powder metallurgy — pure copper and tin powders are sintered together
• Self-lubricating: pre-impregnated with a standard lubricating oil (approximately 30% oil by volume)
• Under many operating conditions, no additional lubrication is required
• In some cases, auxiliary lubrication is recommended to extend bearing life

Performance Factors for Good Operation

• Surface finish of the shaft (journal):
  • Should be a fine ground finish, preferably lapped
• Surface hardness of the shaft:
  • Recommended minimum: steel with 0.35–0.45% carbon content (equivalent to a medium carbon grade)
  • For heavy-duty applications, the shaft should be hardened
• Grade of lubricant:
  • Higher viscosity → longer bearing life
  • However, higher viscosity → greater friction
  • High-viscosity lubricants should only be used with high loads
  • Bearing life can be extended by cutting a grease groove into the bearing and pumping grease in
  • Standard pre-impregnation uses a light machine oil (approximately 20 centipoise at 65°C)
• Heat dissipation:
  • Friction generates heat, which reduces lubricant viscosity and increases wear
  • Housing material and design should promote heat dissipation
  • Example: a thermosetting plastic housing will not dissipate heat as readily as a metallic housing
• Shock loads:
  • Porous bronze bearings handle moderate radial shock loads due to oil-cushioned operation
  • Excessive prolonged radial shock increases metal-to-metal contact and reduces bearing life
  • Large out-of-balance forces in rotating members also reduce life
• Clearance:
  • Bearings are typically a light press fit in the housing
  • A shouldered tool is usually used for installation via an arbour press
  • Running clearance between journal and bush: rule-of-thumb is 1/1000 of the journal diameter
  • Example: 25 mm journal → 0.025 mm running clearance
• Length-to-diameter ratio (L/d):
  • Recommended range: 0.5 to 1.5
  • Too small → high bearing pressure, difficult lubricant retention, side leakage
  • Too large → high friction, potential misalignment causing metal-to-metal contact

Advantages of Journal Bearings (vs. Rolling Element Bearings)

• Low cost
• Quiet operation with minimal noise
• Little radial space required
• High speed capability
• Can operate with non-oil lubricants (water, grease, or even dry/air)

Disadvantages of Journal Bearings (vs. Rolling Element Bearings)

• Relatively low radial load carrying capacity
• Zero thrust load capability (unless a flange type is used with a stepped shaft)
• Low misalignment capability (self-aligning types exist in small sizes but require the misalignment to be taken up between the outer bearing surface and the housing)
• Shaft material and surface finish are critical to performance
• Large sizes (above ~50 mm) are generally not available off-the-shelf

Summary of Best Applications

• Journal bearings are most suitable for relatively high-speed shafts with moderate radial loads and low or zero thrust loads, particularly when cost, noise, and space are important considerations

Thick-Film Lubrication Theory

Lubrication Regimes

• Boundary lubrication: at rest or very low speeds, the journal contacts the lower face of the bearing; considerable wear occurs
• Thin-film (transition) lubrication: as speed increases, oil is dragged around by the shaft, the shaft begins to "float" on a thin oil film; the journal may occasionally contact the bearing (especially during shock loads); moderate wear may occur
• Thick-film lubrication: at high speed, the oil film becomes thick enough that no contact occurs between journal and bearing; no wear occurs because there is no metal-to-metal contact

Frictional Torque vs. Speed

• At rest/low speed: high friction due to metal-to-metal contact (boundary lubrication)
• As speed increases: friction decreases as metal contact diminishes
• Once floating (thick-film regime): friction increases again because fluid friction increases with velocity (as with any fluid flow)
• The most desirable operating point is the region around the onset of thick-film lubrication — below this point, wear occurs and frictional torque is high

Bearing Modulus (M)

• Defined as:

$$M = \frac{\mu \cdot v}{p}$$

• Where:
  • μ = dynamic viscosity of the lubricant (centipoise, cp) at operating temperature
  • v = linear (surface) velocity of the journal (m/s)
  • p = bearing pressure calculated on the projected area (MPa)
• Note: 1 cp = 1000 Pa·s (i.e., 1 centipoise = 0.001 Pa·s)
• Design rule-of-thumb: thick-film lubrication onset occurs at a bearing modulus of approximately 75
  • If M > 75 → thick-film lubrication is likely
  • If M < 75 → consider increasing lubricant viscosity or other design changes to raise M
  • If M >> 75 → thick-film lubrication is assured, but friction will be high — consider reducing lubricant viscosity

Auxiliary Lubrication Methods

• Felt washer soaked in oil with a steel retainer
• Felt wick and oil well arrangement
• Oil reservoir and felt washer (or wool) surrounding the bearing
• Felt pad with spring pressure and a screw cap filled with light grease

Standard Metric Bearing Size Tables

Cylindrical Bearings (Standard Sizes)

Flange Bearings (Standard Sizes)

• Flange bearings have a flange with a specified flange diameter and flange thickness to allow thrust load support and ease of mounting
• Available from 12 mm to 70 mm flange diameter with thicknesses from 2 mm to 5 mm

Non-Standard Metric Cylindrical Bearings

• Available for nominal inside diameters from 3 mm to 25 mm
• Outside diameters range from 5 mm to 30 mm
• Lengths range from 5 mm to 50 mm

Belt Drives

Key Design Notes

• Modern design data is given for wedge belts (not vee belts)
• Pulleys use a taper lock design — when specifying, both the pulley catalogue number and the bush catalogue number are needed
• Belt designation tables give belt length, combined arc of contact, and belt length correction factor
• No specific national standard exists for vee or wedge belts, but commercial products comply with both relevant national and international standards

Context and scope

ANSI/ASME B5.1M-1985 (R1998) — Every Dimension, Every Tolerance, Every Application

The machinist slid the workpiece onto the milling table, dropped a T-bolt into the slot, threaded on a nut, and got to work. Thirty minutes later, the part shifted mid-cut. The cutter broke. The part was scrap.

The diagnosis? He'd grabbed the wrong-size T-bolt for the slot. The head didn't fully seat in the headspace. Under vibration, it rocked, and the clamp loosened. A five-cent selection error cost a morning of production and one expensive carbide endmill.

That story plays out on shop floors across the world — not from ignorance, but from the absence of a single, reliable reference that explains how T-slots, T-bolts, and T-nuts actually work together as a system.

This guide fixes that. You'll walk away with every dimension, every tolerance, every selection principle, and a clear mental model of why this hardware is engineered the way it is.

What Is a T-Slot System and Why Does It Exist?

Picture a machine tool table — a milling machine, a planer, a surface grinder, a jig borer. Its surface is covered with parallel channels cut in an inverted-T cross-section. These are T-slots, and they are one of the most elegant solutions in all of mechanical engineering.

The problem they solve is deceptively simple: how do you hold an unlimited variety of workpiece shapes, sizes, and positions on a fixed table — and then release, reposition, and reclamp quickly — without drilling a new hole every time?

Before T-slots, machinists drilled and tapped holes in their machine tables or used elaborate fixtures for every new part. T-slots changed all of that by providing:

• Infinite linear positioning along the slot length
• Repeatable clamping force via standardized fasteners
• Rapid repositioning by loosening, sliding, and retightening
• Dual-duty capability — the same slot can accept either a T-bolt (dropped in from the end) or a T-nut (a receiver that accepts a standard stud)

The governing standard in North America is ANSI/ASME B5.1M-1985 (R1998), which defines the dimensional chain for T-slots (Table 1), T-bolts (Table 2), and T-nuts (Table 3). Every dimension in this guide comes directly from that standard.

Anatomy of a T-Slot — Every Dimension Explained

Understanding the T-slot geometry is the first step. Below is a labeled cross-section with all dimension designators from ANSI/ASME B5.1M.

          ← A1 (Throat Width) →
     ┌────┬──────────────────┬────┐   ─── Table Surface
     │    │   THROAT         │    │
     │    │                  │    │   D1 (Throat Depth)
     │    │                  │    │
     ├────┤                  ├────┤   ─── Shoulder
     │    │                  │    │
     │    │   HEADSPACE      │    │   C1 (Headspace Depth)
     │    ←──── B1 ─────────→│    │
     │                            │
     └────────────────────────────┘
           ←─────── B1 ────────→
                (Headspace Width)

Dimension Key (T-Slot):

Critical Design Note: The throat dimension A1 is basic — it is the controlling dimension from which all mating parts are referenced. Tolerances are applied to the slot, not subtracted from the nominal size.

T-Slot Tolerances: Holding vs. Location

This is where most machinists and engineers go wrong. The ANSI/ASME B5.1M standard specifies two completely different tolerance regimes depending on the intended use:

When the Slot Is Used for Holding Only

The slot simply needs to grip a workpiece without it shifting under cutting forces. Positional accuracy relative to the machine spindle is not required.

$$\text{Tolerance} = +0.000 \text{ to } +0.010 \text{ inch (inch series)}$$

$$\text{ISO Equivalent} = \text{H12 per ISO/R286 (metric series)}$$

When the Slot Is Used for Location

The slot must precisely position a fixture, tongue, or component relative to a machine datum. Tight tolerances are essential for part-to-part repeatability.

$$\text{Tolerance} = +0.000 \text{ to } +0.001 \text{ inch (inch series)}$$

$$\text{ISO Equivalent} = \text{H8 per ISO/R286 (metric series)}$$

The difference between these two tolerance classes is tenfold. Specifying holding tolerances on a locating slot — or vice versa — is a design error that causes either sloppy fixtures or impossibly expensive machining.

Rule of Thumb: If your fixture uses a tongue or tenon for alignment, specify H8 (location). If you're simply clamping with T-bolts and no positional reference is needed, H12 (holding) is correct and significantly cheaper to machine.

Complete T-Slot Dimensional Tables (Inch & Metric)

Table 1A — American National Standard T-Slots (Inch Series)

ANSI/ASME B5.1M-1985 (R1998)

Throat dimensions are basic. Tolerances applied per intended use (see Tolerance section above).

Table 1B — American National Standard T-Slots (Metric Series)

ANSI/ASME B5.1M-1985 (R1998)

Table 1C — Corner Rounding Dimensions (Inch Series)

Corners of T-Slots may be square or may be rounded/broken to the indicated maximum dimensions at the manufacturer's option.

Table 1D — Corner Rounding Dimensions (Metric Series)

T-Bolts — The Hidden Fastener That Carries the Load

Return to our story. The machinist grabbed the wrong T-bolt, and the head didn't fully seat. Why does the head geometry matter so much?

A T-bolt is not a standard hex bolt that happens to live in a slot. It is a purpose-engineered fastener whose square or rectangular head is designed to:

1. Slide freely along the slot before tightening — clearance between head and slot walls allows positioning
2. Resist rotation when tightened — the head geometry locks against the slot walls and prevents the bolt from spinning
3. Bear load against the slot shoulders — the underside of the head bears against the headspace floor, converting thread torque into clamping force

     ┌─────────────────────────┐
     │    B2 (Across Flats)    │
     │  ┌─────────────────┐    │   ← T-bolt head width must fit
     │  │                 │    │     within headspace width B1
     │  │   BOLT HEAD     │    │   C2 = Head Height
     │  │                 │    │     must fit within C1
     │  └────────┬────────┘    │
                 │ SHANK
                 │ (threaded above table surface)
                 │
                ═══ NUT or CLAMP

T-Bolt Thread Specifications

T-bolts use standard thread forms but specific tolerance classes to ensure proper engagement under the high clamping forces of machine tool work:

• Inch series: UNC-2A thread tolerance class
• Metric series: ISO thread grade 5g 6g (thread grade and tolerance position per page 1764 of the standard)

The 2A / 5g6g classifications provide a small negative allowance — the thread is slightly undersize before plating or coating. This ensures reliable assembly even with standard tapped holes and prevents galling under heavy loads.

Complete T-Bolt Dimensional Tables (Inch & Metric)

Table 2A — American National Standard T-Bolts (Inch Series)

ANSI/ASME B5.1M-1985 (R1998)

Thread tolerance: UNC-2A. T-slots to be used with these bolts: see Table 1.

Table 2B — American National Standard T-Bolts (Metric Series)

ANSI/ASME B5.1M-1985 (R1998)

Thread tolerance: ISO 5g 6g.

Corner Note: Corners of T-bolts may be square or may be rounded/broken to the maximum dimensions shown, at the manufacturer's option. This applies to both inch and metric series.

T-Nuts — The Anchor That Lets You Reposition Without Drilling

Meet the second clamping strategy. Where a T-bolt drops into the slot head-first and threads project upward, a T-nut works in reverse: it slides into the slot tongue-down and provides an internal thread that accepts a stud or bolt from above.

Why Use a T-Nut Instead of a T-Bolt?

T-Nut Anatomy

     ┌────────────────────────────┐ ← NUT BODY (B3 wide, C3 high)
     │   ┌──────────────────┐     │
     │   │   TAPPED HOLE    │     │ ← E3 thread (UNC-3B or ISO 5H)
     │   │   (accepts stud) │     │
     │   └──────────────────┘     │
     └─────────────┬──────────────┘
                   │ TONGUE (A3 wide)
                   │ fits in slot throat
                   │

Dimension Key (T-Nut):

Thread Tolerance Classes for T-Nut Tapped Holes:

• Inch: UNC-3B (high-precision fit — tighter than standard 2B)
• Metric: ISO 5H (medium-precision internal thread)

The 3B/5H classes are deliberately tighter than general-purpose fastener threads because T-nut studs undergo high preload forces and vibration from machining operations. A loose thread fit would allow the stud to work loose under these conditions.

Complete T-Nut Dimensional Tables (Inch & Metric)

Table 3A — American National Standard T-Nuts (Inch Series)

ANSI/ASME B5.1M-1985 (R1998)

T-slot dimensions to fit the above nuts: see Table 1. No tolerances given for Total Thickness K3 or Nut Length L3 — these need not be held to close limits.

Notice the stud thread is one size smaller than the T-bolt size. A 0.500 T-slot uses 3/8–16 studs. This is intentional — the stud shank must pass through the throat, and the tapped hole must fit within the nut body width.

Table 3B — American National Standard T-Nuts (Metric Series)

ANSI/ASME B5.1M-1985 (R1998)

Tapped thread tolerance: ISO 5H.

The T-Slot System — How All Three Components Work Together

Here is where the three tables reveal their elegant engineering logic. Look at the dimensional relationships:

The Sizing Chain

Every component in the T-slot system is sized from the same nominal T-bolt size designation. When you say "1/2-inch T-slot system," you mean:

• The slot throat (A1) is sized for a 1/2-inch T-bolt — throat width nominally 0.562 inch
• The T-bolt has a 0.500–13 UNC-2A thread and a head that fits the headspace
• The T-nut for that slot accepts a 3/8–16 stud through its 0.500–0.562 inch tongue

NOMINAL SIZE DESIGNATION
         │
         ├──→ T-SLOT: Controls throat width A1, headspace B1 × C1, throat depth D1
         │
         ├──→ T-BOLT: Head width B2 fits in headspace B1, head height C2 fits in C1
         │            Thread size equals nominal (e.g., 0.500–13 for 1/2-inch slot)
         │
         └──→ T-NUT:  Tongue width A3 fits in throat A1
                      Stud thread E3 is one size down from nominal
                      Body width B3 fits in headspace B1