Left hand radical (Kangxi #64
手 in its 3-stroke compressed form). Anchors the action:
捆 is to tie up, bind, bundle — a hand gathering and securing things together (
捆绑 bind,
一捆 a bundle). Same radical groups
打 (hit),
拉 (pull),
抱 (embrace),
扣 (button) — hand-action verbs, especially those involving grasping.