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Westfield Fasteners Product Specification:

DIN 603 - Coach Bolts (Cup Head Square Neck Bolts), with Full Thread

This product guide contains the specification for metric threaded coach bolts / carriage bolts, specifically with a fully threaded shank, available from Westfield Fasteners. The basis of this specification is the DIN standard DIN 603.

Product Description
Generally used in timber to timber and timber to metal construction, these bolts incorporate a square neck to grip the hole in the timber when fitting, and therefore negates the need for any drive recess to be included on top of the head. Supplied to DIN 603, but with a fully threaded shank.

Scope of the ISO standard.
DIN 603 specifies the tolerances and the permissable variation in form of carriage bolts / coach bolts / cup head bolts, and covers metric thread diameters from M5 up to and including M20. Mechanical properties for these items are defined in ISO 898 and ISO 3506.

Table 1 below defines the overall dimensions and tolerances of this screw type, whilst table 2 defines the tolerances on the shank length.

technical drawing of Coach Bolts (Cup Head Square Neck Bolts), with full thread to DIN 603

Figure 1: Coach Bolts (with full thread)

Notes to figure 1:

Variations from DIN 603
In practice, the manufacturers often stray away from the standard when deciding how much thread to apply to the shank on these bolts. This is why there are fully threaded variants of many available sizes.

Table 1: Dimensions & Tolerances according to DIN 603

Thread, dM5M6M8M10M12M16M20
thread pitch (standard metric coarse)0.811.251.51.7522.5
head diameterdk max.13.5516.5520.6524.6530.6538.8046.80
dk min.12.4515.4519.3523.3529.3537.2045.20
shank diameterds max.56810121620
ds min.4.525.527.429.4211.3015.3019.16
neck heightfn max.4.104.605.606.608.7512.9015.90
fn min.2.903.404.405.407.2511.1014.10
head heightk max.3.303.884.885.386.958.9511.05
k min.2.703.124.124.656.058.059.95
head radiusr1 ≈ (approx.)10.712.61619.224.129.333.9
neck radiusr2 max.
square neck radiusr3 max.0.750.901.201.501.802.403.0*
neck thicknessvn max.5.486.488.5810.5812.7016.7020.84
vn min.4.525.527.429.4211.3015.3019.16

*The dimensional table from DIN Standard 603:2017-05 states this dimention to be 30mm not 3.0mm, however we believe this is a mistake.

Table 2: Shank Length Tolerance according to DIN 603

shank length (mm)+/- (mm)

For further details, please refer to the ISO/DIN standard document for this item.