I thought I would try making a couple of Graduate magnetic roller ball kits, so I downloaded the relevant PSI instructions, which state that the drill bits needed are 10.5 mm and 12.5 mm, neither of which I had. Foolishly, I splashed out on the relevant Colt drills and used them to drill the blanks, only to discover that both holes were much too big! I then did what I should have done at the start - I measured the diameters of the tubes and found that a 10.0 mm drill was perfect for the long tube and a 15/32" bit was only a little over size for the short tube. An 11.5 mm bit would have been better, but I don't have one.
So, I've just learnt two valuable lessons: (1) don't trust instructions; (2) measure the diameter of the tubes before lashing out on expensive drill bits.
Does anybody know of any kits for which a 10.5 mm and a 12.5 mm drill bit are needed? If not, I have just wasted my money. 
