What do the "Burr Numbers" mean?

[wolfv]

What do the "Burr Numbers" mean? (for die grinder burrs)
The following list of Burr Numbers is from the left column of http://www.pts-tools.com/cgi/CGP2LMXE

SA-1
SA-1L
SB-1
SB-1L
SC-1
SC-1L
SD-1
SE-1
SF-1
SG-1
SH-1
SJ-1
SK-1
SL-1
SM-1
SM-2
SM-3
SN-1
SQ-1

Thanks.

 

[OldMachinist]

Letters are for shape, numbers are size.
http://specialtycarbideburs.com/basic-bur-shapes/sa-cylindrical-bur/

http://www.carbidebur.com/shapes/burs.htm

 

[wolfv]

Thanks Don. The illustrate shapes of carbide burs is nice.