MAINS NUT SET,ARP NUTS COOPER "S"ONLY

Special "S" main bearings nut set (6). On all performance A series engines it is essential to ensure accurate and as near permanent location of the center main bearing of the crankshaft as possible. Flexing allowed here, especially at sustained high RPM levels, can cause spun bearings, crank or main cap breakage with severe or mortal damage to the engine.