clamp, (kokuji)
鎹 is a Japanese kokuji for a metal clamp or staple used to join two pieces of wood. Its meaning is specific to that tool and does not extend to abstract clamping ideas.
鎹 is a Japanese kokuji created by combining 金 (metal) with 送 (send), likely to express a metal piece that sends or joins things together. The exact historical development is uncertain.
The left side 金 is metal, and the right side 送 suggests sending or joining. Picture a metal clamp sending two boards together, holding them tight.
For かすがい, imagine a metal clamp that is a 'casual guy'—it just hangs out holding things together: casual guy -> かすがい.
—