Flange bolts

[Theo Markettos]

I need some replacement bolts for the car, but buying zinc plated flange bolts turns out to be surprisingly hard. The usual suspects (Screwfix, TS, CPC/Farnell, RS) don't have any, nor do I manage to find anywhere sane by googling except for some people with a rather optimistic view of pricing:

TS sell a pack of 700 yellow zinc plated woodscrews for about a penny each, flange bolts can't be that much more, can they? Are they called something else that I'm unaware of? I'm thinking of the things with spanner hex heads (optionally a flathead or crosshead slot too) and a captive washer as part of the head. Anyone suggest good places to go for hardware apart from the above? It would be useful to buy an assortment kit rather than having to specify individual sizes.

On the subject of zinc plating, one of them is for a (non-load-bearing) seat mount that goes all the way through from the cushions to the wheel arch. Of course the outside has rusted solid. Since stainless doesn't seem like a great plan (electrolytic corrosion), wondering about yellow zinc plated steel in some kind of rubber grommet to prevent against electrical contact. Though that might be worse if it lets any water in, especially if it perishes (road oil, etc). It'll be undersealed over the top, but that won't last forever. Or is it better to have it mechanically tight and just live with the fact that it'll rust in moments?

Cheers, Theo

[Phil L]

Is there any reason why you can't just go to a breakers yard and fill your pockets with as many as you like?

[The Natural Philosopher]

Plenty of suppliers of these. Don't worry about corrosion. Car will be dead before you need to undo it.

[Jeremy Nicoll - news posts]

What advantage do these things have over a normal bolt & loose washer? It seems to me that this type of bolt can scratch whatever substance it's tightened against, whereas with a loose washer maybe the washer would turn less?

[Theo Markettos]

Good question, I don't know. One reason is car bolts tend to be in awkward places, and you can guarantee that a non-captive washer is going to drop off and land somewhere unfortunate.

Scratching isn't really a problem for mechanical things - engines aren't designed to look pretty, in fact maybe digging in is an advantage. One reason might be vibration - not sure if a loose washer is more likely to unscrew the bolt over time.

Theo

[Theo Markettos]

It's possible, of course, but needs finding a breakers yard that'll let me do that and a day out. I was hoping just to order a box of 100 assorted, like you can with normal bolts. Can't be that hard, can it?

Theo

[Jeremy Nicoll - news posts]

The latter could possibly be fixed with a 'shakeproof' washer.

After posting my question I wondered if the reason for using the flanged bolts wasn't so much because there's a 'washer' but because a flange spreads the load around a bigger area of whatever the bolt pierces than an ordinary bolt head would do. That might matter if eg it's holding plastic trim down (which I have seen on cars), and it also means the hole in the plastic can be a bit bigger than usual (so the plastic needn't be such an accurate fit) and still look neat when the flange covers that up.

[Theo Markettos]

Care to suggest any? I've failed to find any, but I don't know what the 'Farnell' equivalent in the fasteners world is.

Theo

[The Natural Philosopher]

Google flange bolts.

[Bob Eager]

Try here. They only mention flange nuts, but you could ask them...

[Theo Markettos]

I spent quite some time doing that. For some reason getting stainless flange bolts is easy, but getting zinc plated ones is hard. Stainless would rust the car in preference to the bolt, which is a bad plan. It's odd, because cars are covered in zinc plated flange bolts but they aren't easy to buy. Meanwhile zinc plated woodscrews are everywhere.

Hydraulics people have bolts in M10 or bigger, but I want smaller (M6, M8).

I'm slightly surprised there isn't a big warehouse-type supplier of industrial hardware... what do engineering firms do when they want nuts and bolts?

Theo

[Andy Wade]

SEMS units - e.g.