Key Steel

Key steel stockholders and suppliers, delivering to the whole of the UK. A bright drawn steel in square and rectangular bar, key steel is an unalloyed medium carbon steel with reasonable tensile strength. It is supplied bright drawn in flat and square sections conforming to the specification requirements of BS46 and BS4235.

Imperial sizes of key steel bar are bright drawn to plus tolerances conforming to BS46 “keys and keyways”. Metric sizes of key steel bar are bright drawn to minus tolerances conforming to BS4235 “parallel and taper keys”.

We welcome export enquiries for key steel. Contact our sales office and consult our shipping policy for further details.

Alternative carbon steel grades we supply

EN3 | EN8 | EN9 | EN32 |  EN43 |  070M20 | 080M40 | 070M55 | 080A15 | S275 | S355

Form of Supply

As key steel suppliers West Yorkshire Steel offer rectangular and square bar in 1 metre and 3 metre lengths. Key Steel is a bright drawn carbon steel available in standard metric and imperial sizes (listed at bottom of this page).

  • Flat

Click on the headings below for further information


Key Steel is widely used for many general engineering applications. Typical key steel applications include taper, gibhead, plain and parallel keys.

Carbon0.35-0.45%Phosphorous0.06% max
Manganese0.60-1.00%Sulphur0.06% max

As a bright drawn steel bar it is uncommon to harden key steel. In its supply condition key steel has an approximate tensile strength of 500 to 700N/mm2.

If heat treatment is a requirement, key steel can be heat treated by conventional methods and flame or induction hardening. Please consult your heat treatment provider for full guidance on heat treatment of key steel.

Imperial Squares
Up to and including 7/8”-0/+0.002”
Over 7/8” Up to and inc. 1 ¼”-0/+0.003”
Over 1 ¼”-0/+0.004″
Imperial Flats
Up to and inc. ¾” x ½”Width -0/+0.002”   Thickness -0/+0.003”
⅞” x ⅝”Width -0/+0.002”   Thickness -0/+0.004”
Over ⅞” x ⅝”” up to and inc. 1¼” x ⅞”Width -0/+0.003”   Thickness -0/+0.004”
Over 1¼” x ⅞” up to and inc.1¾” x 1¼”Width -0/+0.004”   Thickness -0/+0.006”
2″ x 1 1/4″Width -0/+0.005”   Thickness -0/+0.006”
Metric Squares (mm)
Up to and inc. 6+0mm/-0.030mm
Over 6 and up to and inc. 12+0mm/-0.036mm
over 16+0mm/-0.043mm~
Metric Flats
8 x 7 up to and inc. 10 x 8Width +0/-0.036mm   Thickness +0/-0.090mm
Over 10 x 8 up to and inc. 16 x 10Width +0/-0.043mm   Thickness +0/-0.090mm
18 x 11Width +0/-0.043mm   Thickness +0/-0.110mm
Over 18 x 11 up to and inc. 28 x 16Width +0/-0.052mm   Thickness +0/-0.110mm
32 x 18Width +0/-0.062mm   Thickness +0/-0.110mm
Over 32 x 18 up to and inc. 50 x 28Width +0/-0.062mm   Thickness +0/-0.130mm

Imperial SizesMetric Sizes
3/16″ sq5/8″ sq4mm sq16mm x 28mm
3/16″ x 1/4″5/8″ x 3/4″5mm sq18mm x 32mm
1/4″ x 5/16″5/8″ x 7/8″6mm sq20mm sq
1/4″ sq5/8″ x 1″6mm x 10mm20mm x 25mm
1/4″ x 3/8″3/4″ sq7mm x 8mm20mm x 36mm
1/4″ x 1/2″3/4″ x 7/8″8mm sq22mm sq
1/4″ x 5/8″3/4″ x 1″16mm x 20mm22mm x 40mm
5/16″ sq3/4″ x 1 1/4″8mm x 12mm24mm sq
5/16″ x 3/8″7/8″ sq9mm x 14mm25mm sq
5/16″ x 7/16″7/8″ x 1″10mm sq25mm x 40mm
5/16″ x 1/2″7/8″ x 1 1/2″10mm x 12mm25mm x 45mm
3/8″ sq1″ sq10mm x 16mm28mm sq
3/8″ x 7/16″1″ x 1 1/4″11mm x 18mm28mm x 50mm
3/8″ x 1/2″1″ x 1 1/2″12mm sq30mm sq
3/8″ x 5/8″1″ x 1 5/8″12mm x 20mm32mm x 56mm
9/16″ sq1 1/8″ sq14mm sq32mm sq
7/16″ sq1 1/4″ sq14mm x 22mm36mm sq
7/16″ x 5/8″1 1/4″ x 1 3/4″14mm x 25mm38mm sq
1/2″ sq1 1/4″ x 2″15mm sq40mm sq
1/2″ x 5/8″1 1/2″ sq16mm sq45mm sq
1/2″ x 3/4″1 1/2″ x 2″8mm x 10mm50mm sq
1/2″ x 1″1 3/4″ sq
3/8″ x 3/4″1 3/4″ x 2″
2″ sq

We recommend you contact your welding consumables supplier who should provide you full assistance and information on welding key steel.

Key Steel is available with a certificate of conformity, if required please request when placing any orders.

Key Steel bar is supplied in accordance with our ISO 9001:2015 registration.