4-1/4" (108MM) Flex Hone 320 Grit Silicon Carbide Commercial Grade Commercial Version engine cylinder hone is for 3.850" to 4.300" BORES Commercial version hone has 50% more globules than the standard Flex-hone Tool is self centering, Tool can be used with a 3/8" or 1/2" chuck portable drill or drill press Made in USA by the best cylinder hone manufacturers. ITEM IS BRAND NEW IN SELF STORING BOX 320 grit, Excellent for cylinder bore re-finishing for re-ringing jobs utilizing performance or moly rings.