Position Count vs. Sibling Headers
The 77311-124-20LF carries 20 positions. The choice comes down to the I/O count your board needs. Another 20-position sibling, the 77311-102-20LF, differs only in overall contact length (0.465" vs 0.480") — the mating pin length is shorter, which affects stack height with the receptacle. For the 77311-124-20LF, the 0.266" mating length gives a standard 0.100" board-to-board spacing when mated with a low-profile socket.
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