coach bolt washer/plate insert

Wig

Coach bolt with a domed head, has a square cross section below the head.
http://www.screwfix.com/p/general-purpose-coach-bolts-bzp-m6-x-100mm-pack-of-100/16837?kpid=16837&cm_mmc=Google-_-Product%20Listing%20Ads-_-Sales%20Tracking-_-sales%20tracking%20url&gclid=CKOVjvXh5rgCFcfJtAod8RUAeg#

I'm thinking it would be a good idea to have a metal plate about 20 - 30mm diameter like a washer with a square hole in the middle.

On one side of the washer in the centre the square hole would be projected outwards, think of it like the end of this http://www.toolreviews.ca/reviews_hand_tools/LV_50K59/LV_50K59_800.JPG
on the back of the washer. This washer would then be hammered into the hole, the bolt fitted nice and snug and then clamped tight.

I doubt if these things exist but do they?

keystone

Google square hole washer. '000s of them out there and yes you can get them with grippy bits on the back (although not quite like you've described) for use with timber posts and suchlike.



technically I think they are called torque washers.

Cheers