Need to know what size the brake caliper bleed screw or valve is on a Honda CX500, GL500, CX650 or GL650’s brake caliper? It is:
M8 x 1.25

As far as we can tell from looking at the parts manuals all of the CX and GL V-twin line use the same bleed screw size for their brake calipers. Need a new one but want something that’ll make bleeding easier? Check out these bleed valves.
The Honda part number for these is 43352-568-003 and they are still available (eBay US, eBay CA
, eBay UK
, eBay AU
, Amazon) as of the time of writing.