Engine main caps hold the bearings that secure your crankshaft in place. Engines use a variety of different quantities of main caps utilizing main bearing cap bolts or studs. While 2-bolt main caps are very common, 4-bolt mains and even 6-bolt mains are the popular choice for high-powered racing and street performance engines for added strength. Pit Stop USA carries a huge selection of Main Cap Fastener Kits for a wide variety of applications at low everyday prices.s!