well
size depends on what kind of bracelet it is
on the Noob V6s bracelet I have it is M1.4x1,7x14mm
on other Sub bracelets I have (ARF, GMF, BP) it is anywhere from 15.5mm to 15.9mm but all of them with M1.4 thread and 1.7mm pin diameter
main differentiator is whether the thread is all the way through the link so you can see the tip of the pin on the threaded side or whether the thread hole doesn't go through
as you can see in the pictures
accordingly, check your bracelet and if you can see the tip of the pin on the threaded side you need M1.4x1.7x14mm (or maybe 15mm)
if you can't you need either a lenght of 15,5 or 15,9mm (or maybe 15mm) lenght depending on the lenght of the thread in the link
having the wrong thread lenght will result in either the pin tip or the screw head sticking out
my advice would be to take one pin out, measure it with a calipher and go from there
Hope this helps