10-32 Screws

[dereklola]

I know the local hardware store has them - but these are to hold my race car together!

Seriously I need some 10-32 flat head, countersunk, with .330" maximum head diameter. Standard such screws have something like .370 diam which won't fit. They are to retain the brake rotor hats to the axle flanges.

Any suggestions? Can only find the standard size at McMaster.

Thx - Derek

[Earley Motorsports]

If nothing available you could always turn the heads down to the needed size.
Graham.

[EYERACE]

grind 'em down and make life easier

[Neil_Roberts]

Even better, modify the mating parts so that standard fasteners will fit.

[dereklola]

- - - modify the mating parts - - -
- - - turn the heads down - - -
- - - grind 'em down - - -

I was all ready to countersink further into the rotor hat until I realized that the increased diameter would run into the drive peg holes - which is probably why the 'small head' screws were used in the first place - thanks Lola!

Turning down the diam would still leave the heads 'sticking up' so that the wheel would not seat properly. I suppose that modifying a countersink bit to the requisite diam would work but finding the right size screws would be a lot easier!

Grinding down the axial height of the heads would work except that the hex hole would then be very shallow and prone to damage when unfastening a recalcitrant screw.

Thanks for the suggestions guys - still hoping that the smaller head screws are available somewhere.

[RobLav]

What's the countersink angle?

[Steve Demeter]

I think if you look closely all those screws do is keep the hat in place from falling off when the wheel is removed. The has should actually be driven by the wheel drive pins and the wheel nut is what holds it in place a=against the real forces. I had a Lola that was that way. If you don't mind hassling with the hats when you take the wheels off should get along just fine without the aforementioned screws.

[dereklola]

- - - all those screws do is keep the hat in place from falling off when the wheel is removed.

Steve - I agree - in fact my fall back position is just to use the three good, old screws left over from my disassembly - two in one side, one in the other! Also the brake pads will help to hold the hats/rotors more or less in place when the wheels are off. Might be fun replacing brake pads though :-)

Derek

(PS spellcheck does not recognize disassembly. nor spellcheck!

[brownslane]

Derek, try Aircraft Spruce....with that said and they are not available, I would install the top hats with the new screws, take a disc to the offending heads and worry about removal later

I have found that one of the best ways to remove a recalcitrant machine screw, especially if the head is stripped is to hit it with the TIG a couple of times....build up a small mount of weld on the top of the screw head. Combined with the heat shock from the welding, the little "mound" of weld will allow you to grip it with vice grips and remove the threaded portion easily. This works great in the shop, not quite so well at the track!

No easy answer, mate!

Best, Tom

[Modo]

put em' in a drill and rub edge against abrasive for a few seconds, or file, or grinder turned on then off to slow, file to preference after ....... (apparantly above u already thought of that, missed that) ........... you have the advantage of many trys with the hardware store screws, other than that a host of screw offerings at MSC or Master McCarr?? ...... can start looking here but may not give you diameter ..... http://www.mscdirect.com/browse/tn/F...114+4287857076 ..... sounds like you may know this already

[Firesmith]

http://www.aircraftspruce.com/catalo...es/ms24694.php

These look like they may work for you.

Mike

[a. pettipas]

another good hardware source… http://www.earlsindy.com/home/

[nulrich]

There are three different angles for countersunk 10-32 screws (at least): 82, 100, and 120 degree. The most common angle used on aircraft and race cars is 100 degree. Industrial supply houses will carry 82 degree head screws. The nominal head diameter on all of them is the same, somewhere between .362 and .385 depending on which standard you use.

If you use an 82 degree head fastener in a 100 degree countersunk hole it will protrude slightly.

The other complication is that because the angle between the angled underside of the head and the flat is quite narrow (40-49 degrees) there is usually a short cylindrical section at the very top of the flat head. Hard to describe, but look at a flat head screw and you'll see it. The "theoretical" max diameter is the diameter the head would be if it were sharp, but there are actually different heights of the "projection" or short cylindrical section. Socket head (Allen recess) flat head screws tend to have a more pronounced projection, slotted head screws often have very little (look at a brass wood screw sometime).

The tolerances for all of these head dimensions are very loose, so you will see substantial variation between head types and manufacturers.

What this means in practice is that it's very difficult to produce a perfect countersink for all different types of fasteners without making the countersink much bigger than it needs to be.

All that said, I've never heard of or seen a 10-32 flat head screw with a diameter as small as .330 inch. It may be a British thing? I would try to measure or fit some slotted head screws.

The MS24693 (non-structural) and MS24594 (structural) flat head screws from Aircraft Spruce that Mike refers to above are all 100 degree head angle with the same .385" max theoretical "sharp" diameter as any other 10-32 screw. Sorry.

Nathan

[dereklola]

Got it:
MS24694 calls for a head diameter of .385 max / .371 min / .327 abs.min. HUH?

Apparently you can have the outer edges of the head flat rather than sharp to a max of .010 which gives the .327 min. dimension. And that seems to be what I have got. This is not quite the same as Nathan's "small protruding cylinder" above the flat of the head, but a similar concept except that it reduces the diameter which is what I need.

Now my only problem is to find such screws with socket heads.

[nulrich]

That is exactly what I was describing above, I guess I didn't do a very good job. The .385 diameter is the maximum "theoretical sharp" diameter which is how big the head would be if it had a sharp corner.

The absolute minimum diameter is how small the head can be if the sharp corner is trimmed to a cylinder the maximum extent.

In practice you'll never find a production fastener anywhere near that small. And it won't really help you since the flat of the head will sit in the same position...or, if your countersink is shallow, the head will sit proud.

Flat head socket head screws usually have the most projection and will stick up higher than cross recess (Phillips head) screws. In my experience.

Nathan

[Phil Creighton]

Sometimes it helps to be older - try 2BA english fastners. Thats what was on lola's - still has 10/32 thread but the socket head size is smaller (5/32)and the head is 0.319. We had them on all the 70's/80's cars and almost always consigned them to the bin, on arrival, to avoid confusing our US cousins......................Try Metric and Multistandard if you get stuck but they may have a minimum.
Phil
Table of sizes I found
http://www.ba-bolts.co.uk/basocketsize.html

[nulrich]

Older and from the UK, apparently! I did suggest it might be a "British thing" earlier. Are there Whitworth threads on those cars too?

Does a 2BA screw really have 31.86 threads per inch or is it a rounding error from converting back and forth from metric?

[dereklola]

I'm told that NASA spent millions researching a perfect thread form and ended up with the same dimensions as Whitworth.

Now I read that BA is/was the most scientific design of screws - apparently was based on mm but defined in 1/1000". How wonderfully British - like sales prices in Guineas even though the currency was Pounds/Shillings/Pence.

http://en.wikipedia.org/wiki/BA_thre...A_thread_sizes

That minor deviation from 32 tpi probably explains why chasing the threads in my axle flange made 10-32s go in better. But why would Lola use 2BA in 1991?????

Phil - that cheapo sheetmetal brake you sold me 30 years ago is still going strong - used it last weekend.

[Phil Creighton]

As one of our US mechanics used to say "to BA or not to BA" with apologies to Bill S.
There really wasn't much 10/32 stuff around in the UK (as you know it here). A 2BA did the job and was available everywhere. The Metric hardware that the UK switched to replaced it over time. I remember us tossing buckets of 2BA stuff and fitting 10/32 hardware on Van Diemens , Lolas and Crossles in the 80's. The whole underside of our Spice Buick in 89 was 2BA till after the first race when we had to remove bits quickly and we found how easily 5/32 strips out. It does not surprise me that a Lola had them in 91!

I think the odd dimensions in the table is merely a cross reference calculation. The British Standards for ' British Association Screw Thread/Miniature' in 1951 are clearer.
Have you also noticed the inverted flare brake fiittings for -3 Hose that are BSP thread and take a 1/4 Whitworth wrench. Ever wondered why that 1/2 or 9/16 wrench didn't quite fit?
Its a bit like still owning a Lucas Bendix tool...............when you need it!
Phil

[a. pettipas]

Have you also noticed the inverted flare brake fiittings for -3 Hose that are BSP thread and take a 1/4 Whitworth wrench. Ever wondered why that 1/2 or 9/16 wrench didn't quite fit

Yes

[EACIII]

Try working on T series MG's. MG purchased the tooling for the engine and it had metric threads. But they wanted the English custumers to be able to work on them with the tools they had already. So the put Withworth heads on the metric threaded bolts. Now over time some of those special bolts get replaced with hardware store metric bolts. And some of the Withworth bolt on the chassis get replaced with inch sized ones. So you need three sets of tools to work on the cars. American, Metric and Withworth. Fun.

Ed

[Phil Creighton]

GM obviously learned from MG and did that too with AF wrench heads on metric engine bolts so mechanics didn't have to buy metric tools at Chevy dealers.
Not just the Brits!!!