I replaced the stainless steel bracelet on my Omega Speedmaster Racing with a rubber Speedmaster band using these spring bars from Barton.  The quality is comparable to geniune Omega spring bars, but at a fraction of the price.  The bars feature tight springs and very pronounced tips at each end that fit tightly into the holes on the watch case. When they find the holes, you can hear the pins click into place. In terms of size, purchase the size that is the exact width of the watch strap where the pin is to be inserted.  The bars are designed longer than the watch strap, to allow for the spring tips to insert into the holes in the watch case. I would not trust the security of my $4800 Omega watch to just any spring bars.