Doe anyone know what the threads are for the screws that hold the window sliders? I need to get a tap and die to clean out the threads in the captive nuts. they're not BSF/BSW/BA or metric, maybe UNF?

My bus number (if any): RML2532

Almost certainly BA Roy

My bus number (if any): RTL 960, RMC 1458, RM 1585 and several RTs

No, not BA at all! They look like 4BA but 4BA screws I've got are different. ISTR reading somewhere they are an odd something 16ths UNF.

My bus number (if any): RML2532

Hi Roy,
I managed to get replacement screws for the window sliders from a company called Clarkenwell Screws, Nuts and bolts. Very helpful guys that work in there, I literally took a sample in there and one of them disappeared out the back and came back in about 20 mins with a replacement. The head is slightly bigger but not in the way of the window and is still a slotted head.
They sometimes write the thread size on the packet, I will check over the weekend and get back to you if you haven't already solved the mystery of the thread size..

Best Regards,
Pete.

My bus number (if any): RML 2463 & RML 2460

Thanks, I've used Clerkenwell Screws many years ago, they were very helpful, for some BSW bolts and bits for a Gothenberg tram a friend was restoring. I suspect these screws are unf.

My bus number (if any): RML2532

Sorry for the delay in responding, but I had to find the tin of window parts.

There are 3 different length but two different threads. I bought some second-hand dies for cleaning the threads before reassembling my ones a few years ago.

Now I would have guessed that they were UNF, but the smaller die is 1/8 BSW and the larger die is 5/32 but not marked. I would not claim to be an expert in threads and cannot confirm if it is BSW or UNF.

Not sure that helps .......

My bus number (if any): RM1368

5/32 sounds more like a UNK thread; the ones I've got are not 1/8 bsw, thanks.

My bus number (if any): RML2532

On the subject of non metric screw and bolt suppliers, I have had an excellent service from:
County Industrial Supplies in Cwmbran Wales. Will almost certainly have those imperial size bolts that can't be replaced by metric on engines and in my case RTL radiators :)

My bus number (if any): RTL 960, RMC 1458, RM 1585 and several RTs

Did we ever get to the bottom of what size the slide screws are? I need some!

My bus number (if any): RTL 960, RMC 1458, RM 1585 and several RTs

Some time ago I had to renew the front brake pipes on an RM, I was more than surprised to find that externally one end they are a thread I had never heard of: BSC British Standard Cycle. Looking at the chart it seems that there is a 1/8" and a 5/32" BSC. Whether the window screws are this I can't say.

https://britishfasteners.com/threads/bsc.html

I have been reliably informed that the thread id 1/8"BSW, however it is now hard to find the set screws. A better option is to re-tap to M3 and that opens up a range of screw options.

My bus number (if any): RTL 960, RMC 1458, RM 1585 and several RTs

Having found a 3/16 UNC screw, this fitted perfectly. I made further enquiries with several fittings suppliers and none can source 3/16UNC pan head screws, nor the captive nuts that go with them. their advice was as your Brian, tap thread to 3mm and start again!

My bus number (if any): RML2532