Am putting together a PC and have run into a problem with the MB/case. The case fan has a 3-hole connector and all system fan connectors on the MB are 4-pin. Case: Fractal Design Define R5 Black ...

SUZCO SUZCO 25 Foot 4 Wire 4-Flat Trailer Light Wiring Harness Extension Kit, 4-Way Plug 4 Pin Male & Female Extension Connector & Wishbone-Style with 18 Gauge White Ground Wire with SAE J1128.

It takes up roughly half of the inside of the connector. Every female USB port has a corresponding plastic piece housing its contacts, which slots into the male connector when you plug it in.