What is the 1-66100-9 and where does it fit?
It's the socket you stock when you're building or repairing a Multimate III+ harness and need the wire-side terminal.
Wire gauge and termination — what it accepts
This socket is rated for 16-18 AWG stranded wire. That's a common range for signal and moderate-power circuits in industrial control panels, relay sockets, and heavy equipment harnesses. The crimp termination is a standard barrel style — you'll need the correct Multimate III+ crimp tool or an approved die set to get the specified pull-force and contact resistance. The stamped construction keeps the per-unit cost down compared to a machined contact, but the trade-off is a slightly lower mating cycle count; tin plating at this thickness handles field-service reconnects well.