ISO 773 is the governing dimensional standard for parallel keys. This page sets out the scope of the standard, reproduces the full size table it specifies, and lists the DIN/ISO/ASME cross-references commonly cited in datasheets and drawings.
ISO 773 — Scope
ISO 773 specifies the dimensions and tolerances of parallel keys. Material, property class, surface finish and packaging are governed by separate documents in the same standards family (for example ISO 898-1 for the mechanical property classes of bolts and screws).
Tolerance & Product Grades
ISO 773, alongside the related DIN 6885 / ISO 773 entries on this site, specifies product grades (typically A or B for fine work and C for general engineering) and tolerance classes for the controlling dimensions. Choose the grade against the precision your application requires.
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 |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Parallel Keys page. Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
Companion Standards
ISO 773 controls only the geometry of parallel keys. The mechanical strength is set by ISO 898-1 (bolts and screws) or ISO 898-2 (nuts); the surface finish is governed by separate finish standards (e.g. ISO 4042 for electroplating). For corrosion testing, the relevant document is ISO 9227 (neutral salt spray).