Sun visor mounting hole size

Hi after having a new head lining fitted I need to re instate the sun visors, I have poked around where the brackets fit into the roof and found the holes and tried a couple of screw sizes to fit the threaded holes but cannot find the correct size, does anybody know what screw sizes they are, I am presuming they are threaded holes see pic

My distant memory tells me they are self tappers. Same as those holding the wooden widow frames in place.

Peter

Thanks Pete
The old girl is getting near completion
Mike

On mine were countersunk self tappers with slight domed heads:

I thank you sir, I did not want to try self tappers if there was a threaded hole under there. and I did not take them off, so did not know, still need to make a wood surround for the sun roof , have you had any experience with this ? getting the profile correct etc ?

Thanks
Mike

I re-taped the holes to fit some slotted screws. My screws happen to be size 8 32 threads per inch, but it could be anything.

The Parts Manual for the '46-'48 cars is very handy on identifying parts.

For the sun visor screws, page 66 under the Sun Visor parts lists
BD.539/6 Screw, Self-Tapping, fixing Sun Visors quantity 4
and at page 91 in the Self-Tapping Screws section of Hardware
BD.539/6 No. 8, 3/4" length Raised Head, Chrome Plated.

Here is what my '38 SS has, each screw held up by the hole it came from.

They are self tapping as there is only sheet steel behind there. Even the hinge bracket for the windscreen is fixed to similar sheet metal, but with screws and nuts.

If you tap a thread into sheet metal that was a self tapping hole, you remove too much metal for using an original self tapping screw and the tapped thread might only have one or two pitches to grip, which is easy to strip. If this happens, your only solution is to use the next size of self tapping.

Rob, Your two screws that hold the triangular clamp together are original and correct. However the domed wood screws are not correct. These should be self tappers into the metalwork and just have slightly domed heads, not wood screws.

Peter

Peter, I understand what you mean, but wood screws normally have a tapered screw thread. These are straight thread, so even though there is an unthreaded portion of the shank, I think they could be described as self tapping screws. All 4 are the same anyway.
BD.539/x in various sizes are described in the Mark V SPC as self tapping raised head chrome plated.
By contrast BD.538/x are self tapping round head black japan.
It’s not clear to me how raised head would differ from round head, unless they mean the unthreaded portion makes the head raised?

Raised head is what I believe is called ‘oval head’ in the US. They were called raised head because they were conventional countersunk heads with the top raised. A round head is just rounded with a flat base. I noticed that the round heads on the Mk IV are almost semicircular in the side view but modern round heads are more like about a third circle. Interesting about the wood screw type with a parallel thread and plain shank.

You would think they are easy to find, however slotted C/S raised / domed head are not common, plenty of slotted with hex drive

They were a common style years ago in the motor trade but are probably only used by traditional furniture makers today. Classic Fasteners in Welland, Sth Australia has a big range of these from 2 gauge to 10 gauge. They are st/stl rather than chrome.

Thanks. Don’t know why mine are round head. Maybe they were all out of the right screws that day. Oval head makes sense in this application.

I found www.classicfasteners.com.au
It looks like I can buy just 4, so now I need to know the size.

I believe the original size was 6 gauge but it could be 8 gauge if a previous owner went a size up. I would buy both sizes to be sure … to be sure …

I Tried 6 gage, too small 8 gauge is the correct size for me, no more than 3/4 long though, I could not find 3/4 so had to grind the tips down on 1" otherwise they bottom out before tightening