novahobby Steel Flex Collet Coupler for 5mm Motor Shaft 4.76mm 3/16 inch Flex Cable rc Boat

Was not too happy with this collet, for some reason it would not hold the cable, it keep slipping around inside of the collet no matter how much I tightened it, so I had to use another type of coupler, it was supposed to have worked on a 3/16-5mm-187. Is it possible that I had the wrong size collet??