Tag: 17-4 bolt failure

Understanding Bolt Lengths

Q: What is bolt grip length vs the threaded length? And which is the total length of the bolt?
 A: Neither the grip length or threaded length provide information on the overall bolt length. The length of the bolt is always measured from under the head of the bolt to the base of the shaft. The only exception to this rule is for a flat head screw. On flat head screws the length of the bolt is measured from the top of the flat head to the base of the bolt shaft.
The grip length is the unthreaded shank of the screw. This is measured on all bolts (except flat heads) from under the head to the start of the threaded section. Though some people ask for a grip length it is more common to request the total length of the bolt then specify the threaded section. For example, you may request a 3/4″-10 x 3″ Long bolt with 2″ of threads. On this bolt the grip length will be 1″ since it is the portion of the bolt under the head that is unthreaded.
 

17-4 H900 Heat Treatment Failure

Q: We have a drawing for a 17-4 1″ bolt that we would like to order which can be heat treated to H900 – H1050. Are there any heat treat conditions that we should avoid? I’ve heard H900 can lead to sudden failure? Is this true?

A:
With the 17-4PH heat treat conditions, you are trading off elongation for higher strength (and hardness). So, an H900 heat treat would be stronger – but have slightly lower elongation and slightly less toughness compared to an H1050 heat treat. So, H900 may be more prone to failures due to shock loads.

Our advice is always to go with the highest heat treat condition allowable to maximize toughness.