That screw on tip is removed for certain applications that the boot has a cross spring wire that snaps in the thread.

Stock Harley OEM wires use the tip on the plug.

Couple more thoughts. You do not state year but older Harleys read the resistance in the plug for timing setting to control knock. Oly Harley's plug has the correct resistance.

If you do use plugs with screw on tips, tighten it with pliers.

I had a set of these in a Toyota 4X4. Had been in there forever. Any wet damp nights, until the truck was hot, it had this strange sizzle noise especially when you got it into 5th gear. For a long time, I thought the 5th gear bearing that is sealed and located in the back area of a AX15 5 speed was going bad.

Was I surprised to find that that tip was loose and the arch had eaten all the threads out of the tip. The sizzle was the voltage jumping the gap in 4 plugs. Probably what happened here.

Add a signature line to your profile similar to my bike line on your bike.

 

+1...old dirt bike trick. Yes a squeeze or two with pliers will work.

Ken

 

i need to know the spark plug gap on a 1980 shovlehead with elect. pick up