[v8hed]

I had to buy some 12pt 5/16 nuts for the corner studs on my SBC oil pan due to clearance issues. I purchased a 12pt 5/16 socket to tighten them with and it's far too small!

What's the story with 12pt fasteners? What socket size do I need to fit these 5/16 12pt nuts?

Thanks.

[heyjude076]

Originally Posted by v8hed

I had to buy some 12pt 5/16 nuts for the corner studs on my SBC oil pan due to clearance issues. I purchased a 12pt 5/16 socket to tighten them with and it's far too small!

What's the story with 12pt fasteners? What socket size do I need to fit these 5/16 12pt nuts?

Thanks.

Are you saying 5/16 thread size? 5/16 nuts (thread size) usually take a 1/2" socket.

[v8hed]

Originally Posted by heyjude076

Are you saying 5/16 thread size? 5/16 nuts (thread size) usually take a 1/2" socket.

I did some Googling and eventually found an ARP link that stated 5/16 12pt nuts take a 3/8 socket. With every size fastener I've dealt with in the past, the size of the fastener is also the size of the socket/wrench you use on it. Why isn't that the case here?

EDIT: Having said the above, I've never really had occasion to deal too much with nuts in the past... is the size of a nut usually synonymous with the thread size rather than the size of the hex?

[Irelands child]

The ARP fasteners will often take a different wrench size then the standard SAE fasteners, so it will almost be a trial and error. I have some 3/8" header bolts that take a 3/8" wrench where a normal would be 9/16". Since the UK kinda went to metric sizing, you will have to own a set of SAE wrenches to work on older American cars and equipment.

1/4"bolt/nut = 7/16" wrench
5/16 bolt = 1/2" wrench
3/8 bolt = 9/16" wrench
7/16 bolt = 5/8" wrench (or 11/16 occasionally)
1/2" bolt = 3/4" wrench

Here's a GOOD CHART that you can print out for your shop wall.

Dave W

[v8hed]

Thanks for the link.

I do have a decent selection of AF/SAE tools, but 99% of my sockets are hex (as opposed to 12 point). Had to go and buy a pricey rail of deep 12 point AF/SAE sockets locally to get that 3/8 12pt!

Up until now, I've always known bolt sizes to be known by the size of the hex rather than the size of the thread. So, a 3/8 bolt would take a 3/8 wrench. What's different here? Is it because ARP fasteners have their roots in aerospace where perhaps the convention is to refer to the fastener size by the size of the thread?

[Irelands child]

I had forgotten why ARP uses smaller headed bolts but here is another link cold heading/grain stucture . You have to read between lines but it is pretty evident why they go this route. Almost every engine I have built has many ARP fasteners and I've never had a single failure. About the 12 point, most of what they offer comes either way, 6 or 12, depending on the use. Every fastener you see here is ARP and 6 point tho a few others on this engine are 12:




Dave W

[v8hed]

Originally Posted by Irelands child

About the 12 point, most of what they offer comes either way, 6 or 12, depending on the use.

I use 12-point where space constraints dictate a hex can't be used. On my engine, I had to use 12-points on the head studs as there wasn't room for a 6-point nut. Also, on my oil pan corner studs, I had to use 12-points. It's only when I started using 12-point fasteners that I realised that regular 6-point sockets aren't 100% compatible! Bummer.