That bolt is very reason K&N filters are banned. They are only to be used to unscrew filter, not to install. When you weld onto thin metal, you overheat area and cause carbide precipitations that makes metal brittle. Over time with pressurizing canister on and off, it will crack at HAZ. By using nut to screw on, you speed up this process of cracking and it will fail at most unfortunate time.
Such as trackday last year at TH. Bike going into T14 loses all its oil in braking zone and takes out 5 other bikes. Totals a very nice Aprilia RSV4 Factory. Another guy breaks both wrists in pile-up. Now many trackday providers are banning all K&N filters in addition to racing orgs.
Yes - I know about the install thing. I remember I learned from my dad that you only use hands to put on oil filters. I am guessing what happens with K&N is that dummies think the bolt is "put on" AND "take off."
In fact, once of my big pet peeves is people who over-tighten things!!! When I got my Royal Enfield, it was used. I remember the first time I went to change the oil and I am thinking "what fricken cretin tightened the drain bolts this tight?" There's actually two. Or five if you count the 3 that hold the oil filter cartridge in.
My dad called it "white torque, red torque, and blue torque."
White torque is just a little more than snug. You can feel the bolt stretch a *tiny* bit. It's adequate for most things. You aren't using much more than the force of your wrist muscles.
Red torque is when you use your arm muscles and your face turns red. That's for things like axles and stuff.
Blue torque is you use your whole body, and your face turns blue - it's for head bolts, and you should be using a torque wrench anyways!!!!
ETA: I know this doesn't seem scientific - but over time, especially after using a torque wrench for years, you just get a feel for how much torque you are applying. My dad's hobby was airplanes. He was a licensed A&P mechanic as well, because he liked to build them. Pretty sure he used torque wrenches on airplanes, but on cars he was like DGAF.
