Bullet wire connectors onmy 40MERC

[Clem Clement]

I struggle on. When a bullet wire end is inserted in a tubular connector, what holds the connection in place. Does to overhanging rubber insulation grip the bullet? I see no spring involved. The bullet shaped head has a indentation past the rounded head for? I want to extend the wires and change bullet head sizes.

I'm replacing the broken dash lights dimmer switch. The bullet heads are too big for the switch mountings. Also the wire harness bullet-headed wires are too sort to get a good grip on the head.
Not enough room to file the heads.