In the Hygrade 657C kits I used from NAPA there was 3 sets of X-rings in the kit. I normally used the square shoulder type x-ring with grooving as it seemed to seal the best or was just alittle thicker than the other ones. But I also rebuilt them using round buna o-rings too I had on hand.

1970 FE5 Duster 360/904/3.91's SOLD 1973 TB3 SpaceDuster 340/4spd/4.10's SOLD Moparless for now but when the opportunity is right I'll have another one.