1.00" rotor size.To reduce rotor scoring, OE changed to a new style housing w/ a larger bore for the outer rotor. The bore was enlarged by .014” and maximum housing to rotor clearance to .024”. It allows for the use of flat-sided or round o-rings.The black o ring is used in the oil pump housing and the red is used on the block sideThis oil pump is featured in our blog post, "Rebuild your Engine during your Winter Downtime." Read it here.The HC71802666 Oil Pump fits equipment brands such as: Case IH, IH/Navistar Engine, International