It's the panel-mount half of a two-piece receptacle — you need the rear section and the crimp contacts separately to complete the assembly. The housing uses a locking ramp for a positive, vibration-resistant mate, and the 0.250" (6.35mm) row spacing gives enough room for 20-14 AWG wire with the matching terminals.
Contacts — What You Actually Need to Order
If you're re-pinning an existing harness, check the wire gauge against the terminal range — the housing itself doesn't restrict wire size, but the contact you choose does.
Mating Plug and Full Assembly
This front section mates with the Universal MATE-N-LOK II plug housing — the matching half is a separate order. For a complete receptacle, pair the 770055-1 front section with the corresponding rear section (e.g., TE 770029-1 for a 12-position full receptacle). The panel mount is snap-in: no hardware, just push it into the cutout until the retention fingers lock.
If 12 positions are more than you need, the 6-position sibling 770051-1 shares the same 3-row layout, 0.250" row spacing, locking ramp, and panel-mount snap-in. For a higher-density harness, the 15-position 770030-1 is the next step up, still in the same 3-row, same pitch family.