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ASME B29.6M-1993 — Steel Detachable Link Chains, Attachments, and Sprockets
🔗 ASME B29.6M-1993 is an American National Standard that establishes dimensions, definitions, and requirements for steel detachable link chains, their attachments, and mating sprockets. The first steel detachable link chain was manufactured in 1897, and its history is nearly as old as farm mechanization itself. For decades these chains have been used almost exclusively by agricultural implement manufacturers for power transmission and conveying on manure spreaders, corn pickers, planters, hay rakes, potato diggers, elevators, and many other machines. The chain is formed from special-analysis steel strip and heat treated after forming to resist wear while providing strength and toughness. In 1951 the ASA Sectional Committee B29 appointed a subcommittee drawn from the agricultural implement industry and the steel detachable link chain industry to develop a national standard; the resulting standard has been revised several times, and this 1993 edition was approved by the American National Standards Institute (ANSI) on September 29, 1993.
💡 Unlike precision roller chain, the defining feature of detachable link chain is rapid detachment — flexing the chain drives the end bar out of the adjoining hook, so links can be opened and closed without tools, which suits quick field maintenance perfectly.
1. Scope and General Framework 📌
The Standard establishes, in the main, only those dimensions that ensure interchangeability of the chains in service, without restricting manufacturers in their overall design. The 1983 revision added the sprocket dimensions that control the surfaces which must properly engage or clear the chain; this edition updates the format and symbols to the current ANSI standards practice. During this revision, No. 45 and No. 67 chains were deleted because they are no longer manufactured, and the definition of minimum ultimate tensile strength (M.U.T.S.) was updated. The body of the Standard is organized in three main sections: nomenclature and definitions for steel detachable link chains, attachments, and sprockets for steel detachable link chains.
Sprockets for use with steel detachable chains are usually made of cast or wrought ferrous material. Wear resistance is frequently designed into the material of the tooth faces. Sprocket bodies come in many configurations — plate, arm, web, flat, dished, and so on — and hubs carrying the mounting bore may project from either side or from both sides of the sprocket body. It is important to note that the Standard covers only the dimensions that control proper engagement with, or clearance from, the chain; all other structural dimensions of the sprocket body are left to the manufacturer.
⚠️ Detachable link chain is the economical choice for low-speed, low-to-moderate-load traction and transmission. It is not intended for high-speed precision drives; where speed, smoothness, and low noise matter, select precision roller chain per ASME B29.1.
2. Link Construction and Definitions 🔧
The Standard defines the following key terms:
- Steel detachable link chain: a series of successively assembled steel links in which the end bars articulate inside the hook. The chain is detached by flexing it and driving the end bar out of the adjoining hook.
- Link: a one-piece steel link consisting of an end bar (A), a hook (B), and two sidebars (C–C); apart from the end-bar/hook articulation, the link has no moving parts.
- Measuring load: the load under which a dry or lightly lubricated chain should be measured for length.
- Minimum ultimate tensile strength (M.U.T.S.): the minimum force at which an unused, undamaged chain covered by this Standard could fail when subjected to a single tensile loading test.
🚨 The minimum ultimate tensile strength is not a working load — it greatly exceeds the maximum force that may be safely applied to the chain. Moreover, the tensile test is destructive: even if the chain does not visibly fail under the M.U.T.S. force, it will have been damaged and will be unfit for service.
3. Chain Number Series and Attachments 📏
This edition retains more than a dozen chain sizes from No. 25 up to No. 72, each with its own sprocket dimension table. A variety of standard attachments are tabulated (Tables 2 through 11) for types A1, A2, C1, C15, G27, HB4, K1, SH, SD, and AS. Chains are closed with a coupler link and coupler pin; the current coupler design allows any link to be used either right-handed or left-handed.
| Chain Size | Sprocket Table | Typical Character and Application | Common Attachments |
|---|---|---|---|
| No. 25 / No. 32 / No. 32W | Tables 15–17 | Small general-purpose drives, light implements | A1, A2, K1, SH |
| No. 42 / No. 51 / No. 52 / No. 55 | Tables 18–21 | Mid-size main series, planting and harvesting machines | A1, C1, C15, G27, SD |
| No. 62 / No. 62A / No. 72 | Tables 22–27 | Larger sizes, heavy conveying and power take-off | HB4, K1, AS, C15 |
| No. 62H / No. 67H / No. 67XH | Tables 25–26 | Heavy (H) and extra-heavy (XH) series | HB4, K1, C15 |
💡 A1/A2 are single/double bent ear plates; C1/C15 are connecting plates of different heights; G27, HB4, K1, SH, SD, and AS cover other functional shapes. When selecting an attachment, verify that its height, hole spacing, and pitch agree with the chain so that the attachment does not interfere with the sprocket tooth faces.
4. Sprocket Tooth Form and Design Elements ⚙️
Sprocket tooth-form design is central to smooth engagement and chain life. The Standard’s tooth-form figures and pressure-angle tables define the geometric relationships of the tooth profile, including the angular relationships frequently referenced in tooth-form design. The principal design elements include:
| Design Element | Definition | Design Consideration |
|---|---|---|
| Pitch | Distance between articulation centers of adjacent links | Sprocket pitch must match chain pitch exactly |
| Pitch diameter | Reference-circle diameter of the sprocket corresponding to the chain pitch line | Calculated from pitch and tooth count per the Standard |
| Caliper diameter | Caliper reference dimension for inspecting the tooth form | Determined together with pitch, tooth count, and pressure angle |
| Pressure angle | Angle between the load direction on the flank and the radial datum | Affects smoothness of engagement, wear, and noise |
| Engagement/clearance dimensions | Dimensions controlling correct contact with, or clearance from, the chain | Included since 1983 and mandatory |
⚠️ The minimum tooth count of a sprocket must not be too low. Too few teeth intensify articulation impact in the wrap, accelerate wear, and cause chain whipping; too many teeth enlarge the sprocket diameter and cost. Select tooth counts from the standard tooth-form tables and favor wear-resistant tooth-face materials.
5. Engineering Practice Essentials 🛠️
- 🔍 Selection workflow: establish transmitted power and speed → choose a chain size (No. series) → select the sprocket from pitch and tooth count → pick the attachment type for the duty → then verify measuring-load and strength margins.
- 🔧 Strength checking: the working load must stay well below the minimum ultimate tensile strength; select from the manufacturer’s catalog working-load ratings and never treat M.U.T.S. as a working load.
- 💧 Lubrication and maintenance: keep the chain properly lubricated; in dusty field conditions clean mud from between links regularly, inspect hook and end-bar wear, and replace the whole chain when needed.
- 📏 Assembly and alignment: keep sprocket shafts parallel and faces aligned; tension the chain moderately — too tight accelerates articulation wear, too loose causes jumping.
- 📋 Interchangeability check: on purchase or replacement, confirm chain number, attachment code, and standard dimensions so products from different manufacturers remain interchangeable.
6. Frequently Asked Questions ❓
❓ Q: What is the difference between detachable link chain and precision roller chain (B29.1)?
A: Detachable link chain uses one-piece stamped links hooked together and can be opened without tools, but its accuracy and speed capability are limited; precision roller chain is built from bushings, rollers, pins, and plates for high-speed, high-accuracy drives. The two are not interchangeable.
A: Detachable link chain uses one-piece stamped links hooked together and can be opened without tools, but its accuracy and speed capability are limited; precision roller chain is built from bushings, rollers, pins, and plates for high-speed, high-accuracy drives. The two are not interchangeable.
❓ Q: Can minimum ultimate tensile strength (M.U.T.S.) be used to select a chain?
A: No. The Standard explicitly warns that M.U.T.S. is not a working load — it far exceeds the force that may be safely applied, and the tensile test is destructive, leaving the sample unfit for service. Select on the manufacturer’s catalog working-load ratings.
A: No. The Standard explicitly warns that M.U.T.S. is not a working load — it far exceeds the force that may be safely applied, and the tensile test is destructive, leaving the sample unfit for service. Select on the manufacturer’s catalog working-load ratings.
❓ Q: Why were No. 45 and No. 67 chains deleted from this edition?
A: Those sizes are no longer manufactured. Deleting low-popularity sizes that closely resemble other existing sizes strengthens the Standard and simplifies manufacturing and inventory.
A: Those sizes are no longer manufactured. Deleting low-popularity sizes that closely resemble other existing sizes strengthens the Standard and simplifies manufacturing and inventory.
🔍 Q: Which sprocket dimensions does the Standard actually govern?
A: Only the tooth-form dimensions that control correct engagement with, or clearance from, the chain — pitch, pitch diameter, caliper diameter, pressure angles, and related tooth-face relationships. Sprocket body configuration (plate, arm, dished, etc.) and hub dimensions are deliberately left to the manufacturer.
A: Only the tooth-form dimensions that control correct engagement with, or clearance from, the chain — pitch, pitch diameter, caliper diameter, pressure angles, and related tooth-face relationships. Sprocket body configuration (plate, arm, dished, etc.) and hub dimensions are deliberately left to the manufacturer.
