Spark Plug Question

[EHLawyer]

Another stupid question, I'm sure.....but here goes.
Replaced existing NGK BPR5ES spark plugs with the exact same plug (They were installed at shop many years ago). #1 and #4 had the cap on the plug itself (I'm sure theres a real name for the tip of the plug that actually screws on and off the threaded tip of the plug), #2 and #3 did not have the cap........All fittings are tight, though #2 and #3 not quite as firm.......#2 and #3 would not fit over the cap..........Any logical explanation for this mystery?

[btchalice]

the cap at the end of the wire must have been replaced
every motorcycle i own has to have the tip removed to fit

[EHLawyer]

I would have thought the same as you, except all of the wires were replaced at the same time, with the same size/style caps......

[btchalice]

maybe they look the same but with a different part number?

[EHLawyer]

I suppose that's possible..........oh well, another mystery of my bike..........