Metallics JCB29 Bolts 3/8-16 X 5 Carriage Blt St-zn (Jar 25)

Drill to clear the shank, which measures 0.360 to 0.388 inch, so a 7/16 inch bit gives clearance and a 3/8 inch bit gives a tight fit. In wood the square neck under the mushroom head is meant to be pulled into the hole so the bolt cannot spin while you tighten the nut from the back side. Neck height is 0.188 to 0.208 inch, so that square only bites into material at least that thick.

Strength on the JCB29 is 60,000 psi minimum tensile and 36,000 psi minimum yield, with hardness of Rockwell B70 to B100. That is low carbon, unhardened fastener territory, which is what carriage bolts are normally made to. It is fine for general bracket, framing and support work, but it is not a high strength bolt, so do not substitute it where drawings call for a higher tensile grade.

Dimensions conform to ASME B18.5-1990, the standard for round head bolts. The measured values back it up: 3/8-16 thread, shank 0.368 to 0.388, head 0.782 to 0.844 inch, neck 0.188 to 0.208 inch. Note for publicly funded work that it is listed as not Buy American compliant and not ARRA compliant, with country of origin given as multiple.

The JCB29 is plain steel with a zinc finish. Zinc plating handles indoor, dry and occasionally damp service well. For sustained outdoor exposure, wet process areas, or anywhere near coastal salt air, go to a stainless carriage bolt instead, since zinc plating will eventually sacrifice and the steel underneath will rust.

Metallics lists the CB and JCB carriage bolts for electrical, plumbing, heating and air conditioning work. Choose a carriage bolt like the JCB29 when you can only get a wrench to one side: the square neck locks the bolt in a wood or punched hole so you tighten the nut alone, and the smooth domed head leaves nothing sharp on the finished face. Use a hex head bolt instead when both ends are accessible, when you need to torque from the head, or when you need a higher strength grade than 60,000 psi tensile.