Nick, One of the reasons for using metric is the fact that it is easier to figure the offsets, but that is not the only reason. Tom produced a very nice box with lid, and the dimensions work out perfectly with metric cutters and bits. We can not match the dimensions using fractional bits and cutters; this is another good reason. Tom has pointed out that the 1-1/2" guide bushing is plenty large enough, basicly a 38 MM. One of the retailers will jump on the band wagon and produce the guides in metric.