Look down beside the filler cap on your windshield washer reservoir, the one with the blue plastic cap, and beside it you will see a little black cap with 6 Nm written on the top. Use a wrench or your hand and unscrew the little black cap. Nothing will come shooting out. It's only to keep dirt out of the stem, which looks like the one on a bicycle. The can of freon you buy that comes with the gauge will snap down onto it. It's a push down kind of mount, not screw on. Everybody has A/C problems with their 850's these days, judging from all the posts on the BB, including yours truly. Dick