This listing is for a set of eight (8) standard size Sealed Power aluminum pistons with pins and a cast piston ring set (Hastings/Perfect Circle/MAHLE) compatible with 1939-53 Ford and Mercury 239ci "flathead" V-8 engines. P/N (8) 1003NP-STD + 51807-STD. Piston specifications are as follows: BORE: 3.1875" (at standard) HEAD TYPE: Crowned head with ring below pin COMPRESSION DISTANCE: 1.519" plus .210" crown PIN STYLE: Floating PIN DIAMETER: .750" RING THICKNESS: 3/32"-3/32"-3/16"-3/16" NOTES: Not factory duplicate; 7.0:1 CR; OE 8BA-6108A; 95-100 HP engines