ARP Fasteners by Size

ARP’s Fasteners by Size section is for builders who need a particular bolt rather than a kit for an engine. Most listings are 5-packs of bolts, in inch sizes from 1/4 to 1/2 in and metric sizes from M6 to M12. Each is either stainless steel or 8740 chrome moly with a black oxide finish, and the head is 12-point or hex.

The listing data is detailed enough to match a bolt to a drawing. It gives the under-head length (UHL), the thread length, the grip diameter, the head height and the wrenching size, and many listings add ARP’s torque value in ft-lbs and Nm. Broached stud kits in M8 x 1.25 are listed here as well.

To choose, measure the depth of the threaded hole and the thickness of the part being clamped. The UHL should be the clamped thickness plus the thread engagement. Keep the engagement short of the depth of the hole, so the bolt never bottoms out in a blind hole. Pick the finish by location, stainless where corrosion matters, and the head by access, since a 12-point head is driven by a smaller socket than a hex head on the same thread.