54 so that the slide rods 60 62 may accurately slide relatively to a rigid frame the sliding being effected by means hereinafter described at the upper end of the bracket 70 a clamping member 72 is disposed having an arcuate cut out conforming to that of the slide rod 60 for receiving the remainder of the circumference of the slide rod 60 i e the portion not received within the top of the block 70 the clamping member 72 is tapped so as to threadily receive two bolts or the like 74 only one of which is illustrated which normally are disposed so that the member 72 is above the top of the bearing blocks 70 to permit the rod 60 to slide however when a cam change is desired to be made as hereinafter described the bolts 74 are threaded further into the top of the bearing block 70 and the member 72 is forced into engagment with the rod 60 and the top of the block 70 to lock the slide rod 60 thereto because the rods 60 and 62 are tied together by clamping block 56 and by two additional clamping blocks 76 and 78 locking of the rod 60 also locks the rod 62 against lateral movement consequently when a cam change is being made the needle bar 26 is locked and its relationship to the loopers or hooks remains unchanged this ensures that when the tufting machine is again operated the needles and loopers or hooks cooperate properly and repositioning of the needle bar 26 is not necessary as best illustrated in fig5 mounted intermediate the bearing blocks.