There are 10 holes of size 3/16 inch (so get some 3/16 brass rod to use for pins and you can get started).
There are 4 bigger holes. I measure 0.395 inches. I find that a 10mm drill passes very nicely through these holse (10mm = 0.394). Some people call these holes 3/8 but that is a pretty sloppy fit as 3/8 is 0.375. Both 13/32 and 7/16 are too big.
There is one lanyard hole at 0.250 inches.
It seems odd that the big holes are metric and the smaller ones are fractional, but that is how it is. I will note that my local woodworking shop has 10mm brass tube handy and affordable. I see plenty of 3/8 mosaic pins, but not so many 10mm (but they are available).
It is also worth noting that a piece of .223 brass fits nicely in the 10mm hole. 10mm brad point drills are available (as are 3/8).
Tom's Knife Info / tom@mmto.org