insert, fit into, attach (a clog thong)
箝 centers on inserting or fitting one thing into another, often with a clamping or pinching action. The specific sense of attaching a clog thong is a narrow application of this idea.
箝 combines 竹 (bamboo) with 拑, which likely contributes the sound and the idea of clamping or pinching. The exact historical development is uncertain.
The top 竹 suggests bamboo tongs or a bamboo tool. The bottom 拑 looks like a hand gripping something. Picture using bamboo tongs to insert or clamp a small object into place.
For カン, imagine a can being clamped shut by bamboo tongs: can -> カン, and the tongs fit the lid tightly.