Indented bolt heads

[Steve L.]

The automotive world seems to like these bolt heads and use them in many places. But what is the purpose of the indent? It adds to the cost of the head because of the extra manufacturing step,

[Timothy B.]

Re: Indented bolt heads

Steve, I think it's just the opposite, the unfinished head is less expensive because the head finishing step is omitted.

[Patrick H.]

Re: Indented bolt heads

Tim,

I'm moderately sure that a plain, flathead bolt like you see in the bins at the hardware store are easier to make and less expensive than ones with an indented/depressed head. There's a reason you see them on cheap items.

Patrick

[Steve L.]

Re: Indented bolt heads

So why do auto makers go the extra step to create a more costly indented head? I don't see the advantage of and indented head.

[Joe L.]

Re: Indented bolt heads

So why do auto makers go the extra step to create a more costly indented head? I don't see the advantage of and indented head.

Steve-----

In the parlance of the fastener world, there's no such thing as "indented head". Those that we refer to thusly are described as "untrimmed head". The other style is described as "trimmed head".

[Steve L.]

Re: Indented bolt heads

Steve-----

In the parlance of the fastener world, there's no such thing as "indented head". Those that we refer to thusly are described as "untrimmed head". The other style is described as "trimmed head".

Maybe I have this backwards, The untrimmed head ( bolt head with a skirt around it) must then be cheaper than a trimmed head. Is this skirt the result of stamping the head info into the top?

[Todd L.]

Re: Indented bolt heads

Do you have a picture? I am not following, and would like to understand. :-)

[Dick W.]

Re: Indented bolt heads

Do you have a picture? I am not following, and would like to understand. :-)

Sems screw/bolt, used for hood hinges, latches, etc Notice the indentation on the head.

This style head is seen on some cylinder head, intake manifold, etc bolts.

[Steve L.]

Re: Indented bolt heads

Joe, you may be right, but if you look at fastner web pages, most refer to this head style as indented and few, if any, refer to untrimmed.

In any case, since no one seemed to answer the purpose of this style of head, I did a search on the web and did find one reference:


Hex flange machine screws most commonly sold
today feature an indentation at the top of the head. This is a byproduct of the
bolt forming process in which the top of the head is pushed inward to help flush
the 6 corners of the hex screw head. However, this results in rounded/blunted
corners, which can lead to premature worn and damaged corners affecting tool
grip. The indentation will also accumulate dirt, oil and other debris after
prolong use.
NBS Fasteners - Technology


So it looks like this is a manufacturing reason. The push the head in to force the material sideways to make sure that the 6 corners are sharp so that the socket will engage better between the bolt head and the socket. It looks like all bolts get this treatment during manufacturing. The trimmed heads get an extra operation to remove the skirt or whatever it it called.