With Comp Cam Pro Magnum Roller Rockers. Part # in question would be arp-300-8247 which would be for use with stud girdles. Reason I ask is because on ARPs website it advertises the shank size as .600". Now it also advertises part # arp-300-8249 as having a shank size of .600" however on summit racing and jegs they advertise arp-300-8249 as having a shank size of .550". Now both Jegs and summit racing carry part # arp-300-8247 however they don't have any information on the item, just that they carry it. So I call ARP to find out what the scoop is and the tech help guy says the shank size is .560 for part # 8247. I call Comp Cams and they tell me that their brand rocker arm nut for stud girdles is .550" and that the pro magnums rocker indentation where the nut touches is .575". So i call summit racing and ask if the gentleman could give me the shank size information for 8247 and after what seems like 20 minutes he tells me the shank size is .600, which makes me think he went to go look on arp's website even tho the person who works at arp told me it was .560.

So basically i'm all kinds of confused (as you probably are) and wanted to know if anybody was using ARP Perma Loc Rocker Arm Nuts and if so what part # and even better if its the same part # as the one i'm looking at. Don't want to spend 160 bux to find out the sh*t doesn't fit when it gets to my house . Thanks guys!!