Guiding sleeve tilt angle in paralleling instruments

To investigate the guiding sleeve tilt angle in paralleling instruments, the diameter of guiding sleeves and drill shanks were measured for a number of instrument makes and Spirko type drill makes. Significant diameter differences between makes were found for drills as well as for sleeves. The guiding sleeve tilt angle changed considerably depending on drill--instrument combination. Selection of an unsuitably dimensioned drill could increase the sleeve tilt angle by about four times. A dimensional standardization of guiding shanks and sleeves is thus recommended.