Everything you need to accurately measure metric bolt diameter, length and thread pitch — so you order the right fastener, first time.
For precision measurements on standard fasteners in the M4–M12 range, we recommend the following tools.
Our own stainless steel measuring tool — designed specifically for metric fasteners. Identify thread diameter, pitch and length on a single device, no separate calipers or pitch gauge required.
Watch the Pro-Gauge in action
For accurate shank diameter and overall length readings in millimetres.
Used to identify thread pitch quickly by matching teeth against the bolt thread.
Helps you align countersunk and flange heads correctly when measuring length.
Three measurements define every metric fastener. Get these right and you'll always order the correct part.
Also known as major diameter
The diameter of a metric bolt is the shank diameter, expressed in millimetres. Because this is approximately the same as the major (thread) diameter, the thread diameter measurement can be used for fully threaded bolts.
Measured from the material surface to the tip
For bolts where the head sits above the surface, measure from directly under the head to the end of the fastener. For countersunk bolts, measure from the point on the head where the material surface sits, down to the end.
Distance between threads, in mm
Metric fasteners use thread pitch instead of a thread count. A pitch of 1.5 means each thread is 1.5 mm apart along the shank. Smaller fasteners generally have a finer thread (lower pitch).
Not all sizes are available in every material. Check the relevant material section — Aluminium, Stainless Steel or Titanium — before placing an order.
Use these reference images to identify the bolt style you need, then click through to shop the range. Material availability is indicated on each card — browse by Aluminium, Stainless Steel or Titanium.
Pair the right washer with your fastener for proper load distribution and finish. Browse washers in Aluminium, Stainless Steel or Titanium.
Quick answers to the most common bolt measuring questions we get from customers.
Use digital vernier calipers to measure across the threaded shank. The reading in millimetres is the bolt's diameter — for example, an M8 bolt measures approximately 8 mm across the threads.
For bolts with a head that sits above the surface (cap head, hex, flange, dome), measure from directly under the head to the tip. For countersunk bolts, measure from the top of the head to the tip, because the head sits flush with the surface.
Thread pitch is the distance between two adjacent threads in millimetres. The easiest way to measure it is with a thread pitch gauge — slide each blade against the threads until one matches perfectly. The number on that blade is your pitch.
It describes a metric bolt with an 8 mm diameter, a 1.25 mm thread pitch and a 20 mm shank length. This is the standard format used across our range.
No. Bodywork Race Spec Drilled bolts, for example, are only available in aluminium, while Cylindrical Head Torx Drive bolts are titanium only. Check the material badges on each product or browse by Aluminium, Stainless Steel or Titanium before ordering.
Download our complete bolt measuring guide as a PDF — handy for the workshop or garage.
Download PDF GuideStill unsure? Try our Find My Fastener tool, or get in touch — we'll help you identify the right fastener.
Allen Key Socket Cap
Countersunk
Dome Head / Fairing
Flanged Hex Head
Race Spec Drilled
Bodywork Race Spec Drilled
Tapered Socket Cap
Cylindrical Head Torx Drive
Flanged Cap Head Race Spec
Flat Washers
Drilled Washers
Countersunk Washers
Cone Washers
