Bolt head marking

[nbpt100]

What can one infer, if anything, from a hex bolt with a concentric circular feature on the top of the hex head? Is it a manufactures mark? If so, who is the manufacturer? Just very curious. Here are two examples. Both are 1/4-20.

 

[jblnut]

Only place I’ve seen bolt heads like that are on old GM engines from the 60-70’s but they’re larger than 1/4”. Not sure it means much other than maybe a manufacturer mark.

 

[rust in the eye]

https://www.electronicfasteners.com/wp-content/uploads/2014/09/northamericanmfgidentificationmarkings.pdf

 

[Byrdnyrd]

Shear Bolts ( for snowblower and other equipment) have a recessed head! They often have a groove cut in the body as well.

Cheers,
BN

 

[nbpt100]

Shear Bolts ( for snowblower and other equipment) have a recessed head! They often have a groove cut in the body as well.

Cheers,
BN

BN you are very astute. Both of these bolts happen to be shear bolts. Not all shear bolts have that feature but these two do. One has grooves cut in the body and the other does not. I do not know if that head marking is coincidence or intentional with some relevant meaning. I have noticed some of the cheap SAE bolts in the plastic cases from Harbor Freight have a similar feature on the heads. I am wondering if these are even weaker than a typical grade 2 bolt and that may be some indicator. It may mean nothing or something all together different? I am still Curious.

 

[mike93lx]

BN you are very astute. Both of these bolts happen to be shear bolts. Not all shear bolts have that feature but these two do. One has grooves cut in the body and the other does not. I do not know if that head marking is coincidence or intentional with some relevant meaning. I have noticed some of the cheap SAE bolts in the plastic cases from Harbor Freight have a similar feature on the heads. I am wondering if these are even weaker than a typical grade 2 bolt and that may be some indicator. It may mean nothing or something all together different? I am still Curious.

When I did a Google image search, it returned some dorman bolts, so that aligns with cheap

 

[dscheidt]

the depressed center saves some material that's not needed for the performance of the bolt while still allowing normal tool fit.

 

[545_days]

the depressed center saves some material that's not needed for the performance of the bolt while still allowing normal tool fit.

My thought as well.