Just a quick thought that's come about from helping to give a couple of colleagues a very brief intro into the basics of dating clay pipe stems using an assemblage of late 17th to mid 18th-century stems...
 
Has anyone ever tried to convert the Harrington clay pipe measurements / Binford formula into metric measurements?
 
Because as a hands on demonstration tool, the only drill bits I can get my hands on quickly are in millimetre diameters.
 
Any of our helpful Canadian colleagues, perhaps?
 
Alasdair Brooks