ISO 773 is the standard cited for parallel keys. This page sets out what the standard controls for this part, reproduces the dimensional table supplied against it, and notes the related designations referenced on drawings.
ISO 773 — Scope
ISO 773 specifies the dimensional requirements for parallel keys. Material, surface condition and any performance rating are set by separate documents specific to this part family — ISO 898-1 and ISO 898-2, which govern bolt and nut property classes, do not apply here.
Tolerance & Product Grades
Tolerances for parallel keys are given as limits on the individual dimensions in the table rather than as a fastener product grade. Where a general-tolerance class is cited on the drawing instead, it applies to the dimensions not otherwise toleranced.
Dimensions Specified by ISO 773
| Shaft diameter range (mm) | Key width b (mm) | Key height h (mm) | Key length range (mm) | Shaft groove depth t1 (mm) | Hub groove depth t2 (mm) | Reference standard | Notes |
|---|---|---|---|---|---|---|---|
| 6~8 | 2 | 2 | 6~20 | 1.2 | 1.0 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 8~10 | 3 | 3 | 6~36 | 1.8 | 1.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 10~12 | 4 | 4 | 8~45 | 2.5 | 1.8 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 12~17 | 5 | 5 | 10~56 | 3.0 | 2.3 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 17~22 | 6 | 6 | 14~70 | 3.5 | 2.8 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 22~30 | 8 | 7 | 18~90 | 4.0 | 3.3 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 30~38 | 10 | 8 | 22~110 | 5.0 | 3.3 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 38~44 | 12 | 8 | 28~140 | 5.0 | 3.3 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 44~50 | 14 | 9 | 36~160 | 5.5 | 3.8 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 50~58 | 16 | 10 | 45~180 | 6.0 | 4.3 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 58~65 | 18 | 11 | 50~200 | 7.0 | 4.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 65~75 | 20 | 12 | 56~220 | 7.5 | 4.9 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 75~85 | 22 | 14 | 63~250 | 9.0 | 5.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 85~95 | 25 | 14 | 70~280 | 9.0 | 5.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 95~110 | 28 | 16 | 80~320 | 10.0 | 6.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 110~130 | 32 | 18 | 90~360 | 11.0 | 7.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 130~150 | 36 | 20 | 100~400 | 12.0 | 8.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 150~170 | 40 | 22 | 100~400 | 13.0 | 9.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 170~200 | 45 | 25 | 110~450 | 15.0 | 10.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 200~230 | 50 | 28 | 125~500 | 17.0 | 11.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 230~260 | 56 | 32 | 140~500 | 20.0 | 12.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 260~290 | 63 | 32 | 160~500 | 20.0 | 12.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 290~330 | 70 | 36 | 180~500 | 22.0 | 14.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 330~380 | 80 | 40 | 200~500 | 25.0 | 15.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 380~440 | 90 | 45 | 220~500 | 28.0 | 17.4 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
| 440~500 | 100 | 50 | 250~500 | 31.0 | 19.5 | DIN 6885 type A / ISO 773 | Type A round ends; B square ends; C one round one square |
Companion Standards
ISO 773 controls only the geometry of parallel keys. Surface finish is governed by separate finish standards (for example ISO 4042 for electroplating), and corrosion testing by ISO 9227 (neutral salt spray). Mechanical performance is set by the standards specific to this part family, not by ISO 898-1 or ISO 898-2, which apply to bolts, screws and nuts.
When to Specify ISO 773
Choose ISO 773 for international engineering work and OEM supply where ISO standards are the contractual reference. It is the default modern specification for parallel keys.
