the smallest oring goes around the outside the fitting and gets covered up by the rubber boot of the fitting , the black oring goes down in the groove of the cooler , the white back up ring goes on top the oring facing out , remember back up ring always on the opposite side of the oil , the snap ring goes in the outter most groove of the cooler ------------I see the snap/tite lock fittings pop off alot , but I do find the majority of the time it is when a hammer is on the machine , especially a hammer with a low nitrogen charge --------- it also seems to happen more on T140's , I have seen a few that blew it off a few times and the cooler and /or the hose had to be replaced , the price actually came down on coolers and they are $360 for the T300 as I did one a week ago , they use to cost a lot more than that , there are a few machines out there that I had the radiator shop weld a #12 JIC male fitting inplace of the snap lock and had a hose made to match , saves money but this takes time which most people I deal with don't have , time is money ----------- the T300's with high flow use a #16 fitting , the T3 without high flow and the T250's use #12 , the T 140 , 180 190's you need the #10 wrench - it can be hard to seperate the fitting and sometimes it pops right off , have tried all kinds of formulas and have yet to find the sure fire way to get it first try ------the fitting on the right side of the cooler when looking at it from the rear comes off more than any other , I usuallly put a heavy duty electrical tie strap that fits between the cooler tubes that go into the side pipe and strap around the fitting to give it some extra support