Used for sizing your printer to EMT Conduit. Each piece contains the "official" size in the middle ring, and provides a -1mm, -0.5mm, +0.5mm and +1mm ring, to allow you to find the right fit. (slip, press fit, etc) EMT 0-5: Used for sizing the OD of a 1/2" conduit (0.706"), and the ID of a 3/4" conduit (0.824") EMT 0-75: Used for sizing the OD of a 3/4" conduit (0.922"), and the ID of a 1" conduit (1.049") EMT 1-0: Used for sizing the OD of a 1" conduit (1.163"), and the ID of a 1-1/4" conduit (1.38") EMT 1-25: Used for sizing the OD of a 1-1/4" conduit (1.51"), and the ID of a 1-1/2" conduit (1.61")If the EMT conduit fits in/over the middle ring, your 3D printer has excellent resolution! (Use the official size when designing parts) If however, your printer is like mine, and needs a "fudge factor" to fit correctly, then you can figure out that correction factor by finding which step it fits on. Sample: Need to find my printer's correction factor for slip fitting over a 1/2 EMT pipe: Created in Alibre - Source files included