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Seapig · 13-08-2021, 04:45

I am looking for a source for large head countersunk stainless steel machine screws around M08 (5/16) 85 - 90 mm or 3 1/2 inches to replace shorter ones in my mooring cleats so I can beef up the backing plates. Preferably hex drive but I am getting getting less picky every day.

The kicker is the head needs to be close to 20 mm to fit my cleats.

The largest I can find at bolt depot has is around 13mm
McMaster Car largest is 16mm
Budget marine doesn't list head size.
Defender biggest machine screw is 1/4 inch
Westmarine doesn't list head diameter

I know lots of people have improved the backing on their mooring cleats so there must be a source out there somewhere.

Thank you for any suggestions

**GordMay** · 13-08-2021, 05:05

Are washers not practical?

SV Siren · 13-08-2021, 05:11

Have you looked into boltdepot.com? I buy some stuff from there, but I am not sure that they will have something that McMasterCarr does not carry.

team karst · 13-08-2021, 05:53

"countersunk", meaning flat or oval head with an angular mating seat?

**GordMay** · 13-08-2021, 05:57

Quote:

Originally Posted by team karst

"countersunk", meaning flat or oval head with an angular mating seat?

Oops! My bad.

Sailing August · 13-08-2021, 06:03

Granger catalog on-line

McMaster-Carr catalog on-line

rwidman · 13-08-2021, 06:04

In my experience, head diameters are pretty much related to body diameters so I doubt you will find anything with a bigger head unless you go to a larger diameter screw.

Can you drill out the cleats a bit to take a 3/8" screw?

mvweebles · 13-08-2021, 06:26

Try Fastenal. They list a 3/8" x 3-1/2" 18-8 SS machine bolt, but do not give head diameter. Looks like you can email them for a more detailed drawing.

https://www.fastenal.com/products/details/0170165

If you really need the larger head - perhaps enlarge the bolt-hole so you can get a 7/16" machine bolt in?

BTW - Looks like you may be in Puerto Rico. Fastenal have stores in a LOT of locations. I picked-up some kit in Tijuana a couple years ago.

Peter

team karst · 13-08-2021, 06:53

Kinda confused here why a large head is needed. To keep it from falling thru the hole or ???
As a coincidence; I was chasing larger headed bolts yesterday. but it was a 1/4" only. Called a truss head or even a "sidewalk bolt", here in hurricane country. But, they are NOT a countersunk head.

EngineerRetired · 13-08-2021, 06:54

If you haven't found what you need try these folks. If they don't have it they will make it. https://us.misumi-ec.com/

They have on-line chat to hep you. Also a phone number.

jimbunyard · 13-08-2021, 06:58

You need to go up to 3/8 shank. These have a head diameter of .728".

https://www.fastenere.com/38-16-x-1-...el-18-8-qty-10

There are many other supplier choices on line.

Dsanduril · 13-08-2021, 07:41

For metric units ISO 10642 sets the head diameter of flathead machine screws =2x nominal diameter for M3 through M12. Above M12 the head diameter becomes a little less than 2x.

For imperial units ANSI B18.6.3 sets head diameters a little less than 2x.

So, you are looking for a special rare beast with a head > 2x bolt diameter.