These extremely handy adjustable chassis inserts from Fonzie RC are the only set of chassis spacers you will ever need! Forget the struggle of choosing 18T,18.5T, 19T etc etc chassis inserts to get perfect gear mesh, simply position the engine to get the ideal mesh and do the bolts up to lock the engine in place These spacers have been proven over the years,even on 71cc big bore engines and no issues. The set of billet inserts come with 4 M5x20 “unbrako” 12.9 strength bolts. The best money can buy!!!