サーキットブロックス™ - 4ワイヤーブロック - E-Blox®

The four-wire block snaps in tight and the connections hold solid even when my son rebuilds his circuits a dozen times a day. It's just one piece, but it's the one that finally got his speaker and light working at the same time.

Grabbed this as a spare after my kid kept yanking the wires loose mid-build, and the four-wire connection clicks in solid every time. Now his circuits actually survive being carried across the room.

The four-wire connection is way more useful than I expected—I can finally branch a circuit in two directions instead of stacking blocks awkwardly. It clicks in as snugly as the pieces that came with my original set. My kid rebuilt his fan project in half the time.