locking pin can be beaten in during these operations of course the tongue 3 is not in place instead of the locking pin any other locking measure may be taken such as a locking member positioned in the range of the channel 13 to press the antifriction insert 1 against the stock rail 2 this member for instance may be a spring supported on the web 4b of the guard rail 4 and on the end section 12 of the anifriction insert disassembly of the antifriction insert takes place in the opposite order first the locking member is removed if the locking member used is a pin it is beaten down all the way through into the space 16 then the antifriction plate is displaced toward the guard rail 4 until the projections 8 are aligned with the hollows 9 and the antifriction insert 1 can be lifted upwardly it is obvious that the path of displacement needed for disassembly is very short and this facilitates the disassembling fig3 is a top plan view of the antifriction insert shown in fig1 and 2 essentially this embodiment is characterized in that there are three projections 8 each at the two longer sides of the frame 7 fig4 shows a top plan view of a second embodiment of the antifriction insert similar to fig3 here the antifriction insert has three projections 8 at one side only while it comprises a chamfer 19 throughout the entire longitudinal direction at the opposite side the base member 5 accordingly has one continuous groove at one side while the groove at the opposite side has the three hollows 9 in this case the antifriction insert having been properly oriented with respect to the base member 5 is inserted from above first such that.