Guide bushes according to this document are used for surface milling with hand milling machines. They are intended to guide the milling cutter along a profile given by a milling template.
DIN 65227:1992 history
1992DIN 65227:1992-11 Aerospace; workshop facilities; guide bushes for hand milling machines, clearance 2,5 mm
1992DIN 65227:1992 Aerospace; workshop facilities; guide bushes for hand milling machines, clearance 2,5 mm