Cut Threads Vs Rolled Threads
The threads of a mechanical fastener can be produced one of two ways. Either the threads can be cut or rolled. This applies to all types of headed bolts, anchor bolts, etc.
Rolled threads are cold formed by using dies and high pressure. As the pressure is applied the steel grains flow out to create the threads. It is important to note that rolled threading starts with reduced diameter material. For Example, a 1” diameter bolt is manufactured from .912” bar. This “pitch diameter” material is approximately the midpoint between the major diameter (peaks) and minor diameter (valleys) of the threads. The result is a fastener with a full 1″ diameter threaded portion but a reduced body diameter (.912).
Roll threading is an extremely efficient process and often results in significant cost savings. Therefore, most manufacturers will roll threads whenever possible.
Thread cutting is a process where the steel is cut or physically removed from full diameter material. So, in this case, a 1” bolt is made from 1” material creating a full-bodied bolt.
Q & A
Do Roll threads meet all ASTM Specifications?
Technically, except for the structural specifications A325 & A490, all other specifications allow for use of rolled threads with a reduced body bolt.
Is a bolt with a reduced body weaker?
The weakest point on a fastener is the minor diameter of the threads. Since the thread dimensions of cut thread and rolled thread fasteners are identical, there is no difference in strength at all. Because of the work hardening that occurs when rolling threads, it could be argued that rolled threaded fasteners are stronger even though they have a reduced body.
Cost saving Tip
Allow the manufacturer to decide which method to use. Only specify cut or rolled threads when necessary. A lot depends on available material and machinery. The manufacturer is the best one to decide which method is most efficient for your project. If you ask for the wrong method to be used, the price and lead time could be drastically impacted.
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