The 2-644861-8: This is a single-row, 8-position vertical header from the MTA-100 series, on a 0.100" (2.54mm) pitch — the standard spacing for many wire-to-board applications. The shrouded 4-wall design and friction lock mean it mates positively with the matching MTA-100 receptacle housing and stays mated under vibration, unlike an unshrouded breakaway header that can walk loose.
The 0.100" (2.54mm) pitch and 8 positions are the first check against your PCB layout. The through-hole solder tails are 0.140" (3.56mm) long, and the overall contact length is 0.440" (11.18mm) — these dimensions matter for board thickness and clearance on the solder side. Compared to the 4-position, 2-row peer 1-1871673-2 (0.098" pitch, detent lock, board lock), this 2-644861-8 is a simpler single-row friction-lock header with no board lock feature — a direct swap is not possible without changing the PCB footprint.