Muddz

I have a pair of speed bleeders screws with dimensions 3/8"-24 x 1-3/16" that fit a pair of Raybestos front disc brake calipers

I'm looking to purchase a pair of the speed bleeder for a pair of new Raybestos rear drum cylinders. However I'm not quite a hundred percent certain of the rear cylinder bleeder screw size.

They rear cylinders bleeder screw appears to be an 8mm (8mm head)

Speed bleeders I've found in various sizes e.g.

8 mm x 1.0 (thread pitch)
8 mm x 1.25 (thread pitch)
5/16 x 24 (thread pitch)

Using a micrometer on a bleeder valve that came with the Raybestos rear cylinders

Measures ~7.73mm at the widest point on the threads and the nut measures 8.13mm, however I don't know the thread count such as 1.0 or 1.25.

There's approx ~9 threads within ~9.5mm of threads. Overall length of the rear bleed valves that came with new brake cylinders is ~28.84mm or ~1.135 inch.

Muddz

Went to the hardware store and a M8 x 1.0 nut seems to fit the bleeder screw for the rear brakes the best. I don't know the bleeder screw started to easily thread but then stopped about half way down.