The square nuts (fenders, running boards, etc. have a concave side and a convex side. My thought was to install with the side raised where the threads meet towards the surface. Using the other side the four corners would be raised and scratch the painted surface. Any thoughts?

I like your idea. It makes sense, but that may be why we are wrong.

Well... you asked for our thoughts....

I'm thinking that since almost ALL installations of these also included a lock washer, that the concave side of the nut was a microscopic way to tighten down on the outer edge of the lock washer.

Don't know... and heavens forbid... but hopefully NOTHING that you tighten with a square nut is all that critical. But, I understand your concern with scratching the paint. If you look very, very, very closely on my car, you just "might" see some "stuff" in certain areas between the nuts and the painted body surface.... Not everywhere... just in a couple of key (or highly visible) areas.



--bb

Considering you will use a flat washer & a lock washer the pointy end of the square nut would never come in contact with the painted surface...Joe

Just as a side note, my 32 had a few of these square nuts with the concave side with "points" on each corner. I have restored quite a bit of "brown" furniture like quarter sawn oak tables. These types of nuts were used in the assembly of this furniture and were used to "lock" the nuts into the wood when used on bolts and studs. When I rebuilt our 32 sedan, I used flat washers under these type of nuts.

Mac

In all of the '31 & '32 Chevys that I have disassembled the square nuts were just simple both sides parallel square nuts. The nuts with points on one side rounded off are more heavy duty than the ones that Chevy used. Split lock washers were installed under the square nuts so the nut does not actually contact the metal or flat washer.

Same here. All of the original square nuts that I have removed from 1929-32 cars and related parts were simple square nuts without being concave or convex. Also, many of the square nuts were not totally square with two opposite sides having a slightly different dimension than the other two opposite sides. And some were so crude in size that a metric open-end wrench had to be used to remove the square nuts.

i agree with the dog and chipper. mike

On my 29 & 30 all the Original Square Nuts had parallel (FLAT) top and bottom surfaces. All the Replacements one that I have bought have one flat side and one rounded/ angle side.

Based on the Engineering Handbook, the Flat side goes down towards the surface, as this provides the most contact surface area to distibute force and laod, and helps ensures a secure hold. and as stated aboe most all use some sort of washer in between so you should be ok on scrating and tearing up the surface.

Just my 2 cents, granted it may not be worth that anymore :)

Looks like the four square side comes out on top! Or with abutting the surface with washers as well.
I am replacing original fasteners for the sake of extending preservation by using stainless steel as opposed to original steel, the original steel fasteners do hold up very well against them elements and in addition provide a catalyst for rust on body parts.
Now the question is to grind the stainless steel square nuts flat or not? This would alter the thickness and change the weight as well, but I don't think it would effect the integrity of the connection.

The rounded square nuts are not correct for a 30's Chevy.

A piece of square steel bar can be cut and tapped to make the flat nuts if you have access to cut off saw.

I haven't found (nor really looked much) for stainless flat square nuts. Did find flat square nuts in steel, plated steel at McMaster Carr. I am sure there are others too. A few years ago I ordered a bunch through my local hardware store.

Yes, McMaste Carr & Grainger still lists the Square "Flat Top" or "Machine Screw" Nut in their catalog, but not in Stainless !! Grainger also offers them in Galvenized. Fastenal Offers Square Nuts, but only have the Flat Top/ Machined for the smaller sizes, like #8, #10, not for the 1/4-20 !! Only the round tops when you get to that size. MSC Direct offers only Round top Square Nuts...

McMaster Carr: Square Nuts - Flat Top
If you have the Paper Catalog it is on Page 3169

Grainger: Square Nuts - Flat Top
If you have the Paper Catalog it is on Page 3174

Fastenal: Square Nuts

MSC Direct: Square Nuts

These are the guys we work with, and I searched for Parts...

Also Looked at these guys online:

Bolt Depot: Square Nuts

You can get them in stainless (Fastenal, Bolt Bepot), however they are round tops !! I ordered some from Fastenal for a project i was working on, were nice quality and looked great...

Try Jim Gillen in Westford Ma. 978-692-2421

I am leaning towards using stainless grinding the rounded side flat, use lock washers and a flat washer all being painted then add a film of PTFE plastic to the flat washer where it contacts the painted steel fender. Also adding a film washer on the screwhead side as well. This will hopefully slowdown the natural effects of corrosion.

You will most likely have to do a little extra prep on the stainless pieces for the paint to stick good.

Stainless does NOT like to be painted... may go on but does not like to stay !!

I would go with the regular flat steel square nuts and then paint them as planned.

When shopping for 1/4-20 square nuts, keep in mind that newer ones are only 7/16 of an inch across the flats, whereas the ones that came off the old Chevys are closer to 1/2 inch across the flats.

Cheers, Dean