#m makes many different versions of high quality "Scotch Locks" used in many different industries including communications, I first ran into them in the mid 1960s working for a telephone company in SO CA, they offered a number of different types that never failed if used properly You need to know that all of our voltage and amperages were very low, 52 Volts D.C. max, except for the ringing currents, and very low milliamps.