I have had mixed success with the Scotchlok packs.
A few years back I found myself needing to splice UF on 3 occasions within a few of months of each other. The first couple of times the Scotchloks worked great. Set up like concrete. A few months later I tried to use a pack and it wouldn't set up. Tried another and another with the same results. Went across town to a different wholesale house and bought some or theirs. Same results.
I'm guessing that 3M must have let a bad batch out. The funny thing is that I haven't noticed them on the shelves of either supply house since.
