Key Stock Quick Reference Guide

Understanding the standards and tolerances (permitted variance) of key stock can be complicated. Key stock is called out by nominal or named size. Among squares and flats, tolerances are referred to as “oversize” (over nominal) or “undersize” (under nominal).

Actual size is nominal to less than nominal.

Common Names:
Bar Stock; Redi‑Key; Key Bar Stock; Machine Key Bar Stock; Broad Key Stock; Negative Key Stock

Applicable Standards:
ANSI B17.1, Class 1 fit; Metric DIN 6880 for key stock; DIN 6885 for machine keys

Fabrication:
Typically cold drawn. DIN may be polished to make bright.

Common Grades (AISI and DIN References):
1018; 1045; 1060; 4140; SS303; SS314; SS316; DIN 6880; A2; A4; DIN 178; DIN 179

Common Uses:
Used in field applications for repair, with no filing normally needed.

Comments:
Some commercial tolerances deviate from the ANSI spec. Plated parts are marked with the size. Plating normally adds .0005″ to the height and width. Relatively free fitting bar stock keys. Only applies to parallel keys.

Actual size is very slightly over nominal.

Common Names:
Moltrup Steel; True Key Stock; Bright Steel; Close Key Stock

Applicable Standards:
ANSI B17.1, Class 2 fit

Fabrication:
Typically cold drawn. May be polished to make bright.

Common Grades (AISI and DIN References):
1045; 8630; 4140

Common Uses:
Most popular in original equipment manufacturing due to precision finish and tight fit in key way.

Comments:
This is true +.0010″ Class 2 ANSI spec key stock with tight tolerances. Material is difficult to draw and is not always easy to find in the U.S.

Actual size is nominal to greater than nominal.

Common Names:
Bar Stock; Redi‑Key; Key Bar Stock; Machine Key Bar Stock; Mak‑A‑Key™; Close Key Stock; Plus Key Stock

Applicable Standards:
None known, though popularized as Mak‑A‑Key™

Fabrication:
Cold drawn steel.

Common Grades (AISI and DIN References):
1018; 1045; SS303; SS304

Common Uses:
Based on Mak‑A‑Key™ specifications, which require filing in the field for repair applications.

Comments:
Used when a custom fit is required or desired for an oversize key way, for field repairs, or in worn key ways.

Actual size can be above or below nominal.

Common Names:
Bar Stock; Mak‑A‑Key™

Applicable Standards:
Depends on material grade. ASTM 829; ASTM 484; ASTM 582; ASTM B16; ASTM A276

Fabrication:
Cold drawn material. Some nonferrous may be extruded.

Common Grades (AISI and DIN References):
1095; 6061; CDA 360; some grades of stainless steel.

Common Uses:
Typically used in field applications for repair.

Comments:
Does not match ANSI spec, and is a frequent source of confusion. Most desirable grade in maintenance repair operations, and has wide acceptance, but limited commercial availability.

T‑form, offered in both oversize and undersize tolerances.

Common Names:
Offset Key Stock; Repair Key Stock

Applicable Standards:
Sizing aligns to ANSI B17.1 Class 1 fit, bar stock.

Fabrication:
Cold drawn steel. Milled for step and to size; usually plated and marked with size.

Common Grades (AISI and DIN References):
1018; 1045; SS304; SS316

Common Uses:
Used in repair of damaged key ways in shafts, sprockets, and pulleys.

Comments:
Step key stock is often erroneously called “offset key stock,” which generally refers to “Z” shaped rectangle key stock machined with inverse steps on opposing faces.

Round form, with undersize tolerances.

Common Names:
Round LInear Shaft; Round Bar; Round Stock; Rod; Round Axle; Mak‑A‑Pin

Applicable Standards:
Depends on material grade. ASTM A108; ASTM A681; ASTM A686

Fabrication:
Cold drawn steel. Sometimes turned and polished.

Common Grades (AISI and DIN References):
1018; 1045; O‑1; W‑1; 1095; SS303; SS304; 6061; CDA 360

Common Uses:
Versatile material used as shafting, straight pins, rails, or for locating in a wide range of applications and industries.

Comments:
Round key stock is not drill rod. Drill rod is precision ground to size and surface finished.

Hex form, with undersize tolerances.

Common Names:
Hex Bar Stock; Hexagon Shaft; Hex Shaft Stock; Hex Stock; Hex Rod; Hex Axle

Applicable Standards:
ASTM A108

Fabrication:
Cold drawn steel.

Common Grades (AISI and DIN References):
1018; 1045; 8630; 4140

Common Uses:
Machinery, gears, machine parts, structural components, automobile parts, axles, and drive shafts.

Comments:
The primary benefit of hex key stock is that there is no key needed and no key way to cut which saves machining time.

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