I measured a Starboard one at 9.3mm (0.36") major dia which is a bit under 3/8 so i was confused
But given a thread clearance maybe it is 3/8??
and with a ruler (not a pitch gauge) appears to be about 20tpi.
so 3/8BSF (3/8 x 20tpi) may be it.??????
Yep, 3/8" Whitworth.
I often run a tap through them to free them up as they sometimes feel done up but they aren't.
I have one Mistral / Naish board that is 6mm though.
Select to expand quoteMark _australia said..
I measured a Starboard one at 9.3mm (0.36") major dia which is a bit under 3/8 so i was confused
But given a thread clearance maybe it is 3/8??
and with a ruler (not a pitch gauge) appears to be about 20tpi.
so 3/8BSF (3/8 x 20tpi) may be it.??????
What? There's something you don't know? 
^^^ nah just don't have a pitch gauge 
Thanks guys, pleasant surprise that patio bolts fit.
