CADXChange

ResourcesDWG symbol libraries

Free AutoCAD thin parallel keys (DWG) after ISO 2491: 5 x 3 to 36 x 12, forms A, B, C

Thin parallel keys and keyways: 593 ready-made AutoCAD blocks (DWG), free to download and use in your own projects, as a ZIP or one symbol at a time.

593 blocks at real size: the 14 key sections of ISO 2491 from 5 x 3 to 36 x 12 in form A (both ends round), form B (both ends square) and form C (one end round), each in every length of its range between 10 and 400 mm with side view, plan view and section, plus one keyway section per key with the shaft, the key and the hub keyway.

Version 1.0 · updated October 30, 2026 · Check out what's changed

Download ZIPPreview in browser

Using AutoCAD 2017 or an earlier version? Download the 2010 format

Copyright CADXChange. Use and modify the symbols freely in your own drawings and projects, including commercial ones; credit and a link are needed only when you publish them. Please do not redistribute or resell the library. Each ZIP holds one plain DWG file in AutoCAD 2018 format and a README; no add-in needed. Provided as is, without warranty. Library terms (CXL-1.0)

Related symbol libraries

All 593 symbols

593 of 593 symbols

Missing a symbol? Tell us which one.

Attributes for parts lists

The invisible attributes of a key are DESIGNATION (for example A 8 x 5 x 40), STANDARD, FORM, WIDTH_TOLERANCE (h9), THICKNESS_TOLERANCE (h11), CHAMFER, MATERIAL, FINISH, PART_NO, MANUFACTURER, QTY and REMARKS. A keyway block holds SHAFT_DIAMETER, DEPTH_T1, DEPTH_T2, the width fits WIDTH_FREE, WIDTH_NORMAL and WIDTH_CLOSE, and RADIUS.

How to use the library

  1. Unzip the file and open the DWG. Copy the symbols you need into your plan, or drag the blocks in from DesignCenter (ADCENTER).
  2. The blocks are drawn at real size in millimetres, 1 drawing unit = 1 mm. A key shows the side view with the chamfer lines, the plan view below it and the section to the right. Insert it at 1:1; the insertion point is the lower left corner of the side view.
  3. A keyway block is the section through shaft, key and hub keyway, drawn at the shaft axis for the largest shaft diameter of its row in the table; only the part of the circle around the keyway is drawn. The shaft diameter range and the depths t1 and t2 are in the attributes.
  4. The groups are the 14 key sections (the three forms in every length) and the keyways in shaft and hub. The lengths follow the standard: 10, 12, 14, 16, 18, 20, 22, 25, 28, 32, 36, 40, 45, 50, 56, 63, 70, 80, 90, 100, 110, 125, 140, 160, 180, 200, 220, 250, 280, 320, 360 and 400 mm, within the range given for each section.

About the standard

ISO 2491 specifies thin parallel keys and the corresponding keyways in shaft and hub for cylindrical shaft ends, for special applications such as keying in thin walls; for normal cases the standard refers to the normal parallel keys. It gives the key sections b x h for shaft diameters from 12 to 150 mm, the width tolerance h9 and thickness tolerance h11, the chamfer, the length range of each section, the three forms A, B and C, steel with a tensile strength of at least 590 N/mm2, and the keyway widths for free, normal and close fit, the depths t1 and t2 and the radius.

The blocks are our own drawings from the standard tables, not copies, and the library is not certified. The chamfer is drawn with its maximum value, and the keyway uses the nominal width of the key for the walls.

What changed in each version

Version 1.0 · October 30, 2026

New symbols (593)

Thin parallel key ISO 2491 A 5 x 3 x 10 · Thin parallel key ISO 2491 A 5 x 3 x 12 · Thin parallel key ISO 2491 A 5 x 3 x 14 · Thin parallel key ISO 2491 A 5 x 3 x 16 · Thin parallel key ISO 2491 A 5 x 3 x 18 · Thin parallel key ISO 2491 A 5 x 3 x 20 · Thin parallel key ISO 2491 A 5 x 3 x 22 · Thin parallel key ISO 2491 A 5 x 3 x 25 · Thin parallel key ISO 2491 A 5 x 3 x 28 · Thin parallel key ISO 2491 A 5 x 3 x 32 · Thin parallel key ISO 2491 A 5 x 3 x 36 · Thin parallel key ISO 2491 A 5 x 3 x 40 · Thin parallel key ISO 2491 A 5 x 3 x 45 · Thin parallel key ISO 2491 A 5 x 3 x 50 · Thin parallel key ISO 2491 A 5 x 3 x 56 · Thin parallel key ISO 2491 B 5 x 3 x 10 · Thin parallel key ISO 2491 B 5 x 3 x 12 · Thin parallel key ISO 2491 B 5 x 3 x 14 · Thin parallel key ISO 2491 B 5 x 3 x 16 · Thin parallel key ISO 2491 B 5 x 3 x 18 · Thin parallel key ISO 2491 B 5 x 3 x 20 · Thin parallel key ISO 2491 B 5 x 3 x 22 · Thin parallel key ISO 2491 B 5 x 3 x 25 · Thin parallel key ISO 2491 B 5 x 3 x 28 · Thin parallel key ISO 2491 B 5 x 3 x 32 · Thin parallel key ISO 2491 B 5 x 3 x 36 · Thin parallel key ISO 2491 B 5 x 3 x 40 · Thin parallel key ISO 2491 B 5 x 3 x 45 · Thin parallel key ISO 2491 B 5 x 3 x 50 · Thin parallel key ISO 2491 B 5 x 3 x 56 · Thin parallel key ISO 2491 C 5 x 3 x 10 · Thin parallel key ISO 2491 C 5 x 3 x 12 · Thin parallel key ISO 2491 C 5 x 3 x 14 · Thin parallel key ISO 2491 C 5 x 3 x 16 · Thin parallel key ISO 2491 C 5 x 3 x 18 · Thin parallel key ISO 2491 C 5 x 3 x 20 · Thin parallel key ISO 2491 C 5 x 3 x 22 · Thin parallel key ISO 2491 C 5 x 3 x 25 · Thin parallel key ISO 2491 C 5 x 3 x 28 · Thin parallel key ISO 2491 C 5 x 3 x 32 · 553 more

Frequently asked questions

Which key goes with which shaft diameter?
The table of the standard pairs them: shaft diameters over 12 to 17 mm take a 5 x 3 key, over 17 to 22 mm a 6 x 4 key, over 22 to 30 mm an 8 x 5 key, and so on up to over 130 to 150 mm with a 36 x 12 key. The attribute SHAFT_DIAMETER of each keyway block gives the range.
What do the forms A, B and C mean?
Form A has both ends round, form B both ends square and form C one end round and one end square. The round ends have a radius of half the key width, and the form is the first part of the DESIGNATION attribute, for example A 8 x 5 x 40.
Can I use the symbols in commercial projects?
Yes. They are free to use and modify in your own projects, including commercial ones. They are provided as is, without warranty. Please do not redistribute or resell the library; see the library terms.
Are the normal parallel keys included?
No. This library holds the thin keys of ISO 2491 and their keyways. The standard keys for normal cases are a different standard and are not part of it.
Can I change a symbol or add attributes?
Yes. Open the DWG, edit a block with BEDIT to change it or add attributes, and save. To update drawings that already contain the block, run ATTSYNC or replace the block. Make a backup first: attribute values can be lost if ATTSYNC is used carelessly.
Where do I find a ready-made set of these symbols for AutoCAD?
AutoCAD itself ships only a small set of sample blocks, so a full symbol set has to come from a library. Download the ZIP on this page and open the DWG: every symbol is a block. Insert one with INSERT (Blocks palette, Libraries tab, then pick the DWG) or drag it from DesignCenter (ADCENTER). You can also download a single symbol on its own.