Explanation:

- Option 1: Swimming

- Swimming doesn't typically use a bolt as a piece of equipment. The sport mainly involves swimsuits, goggles, and swimming caps.

- Option 2: Mountaineering

- ?? This option is correct.

- Mountaineering often uses equipment bolts. These bolts are crucial for creating secure anchor points on rock faces, ensuring climbers' safety.

- Option 3: Cycling

- Bolts in cycling are part of the bike's construction. However, they are not described as essential sporting equipment in the context of the sport.

- Option 4: Motor sports

- Bolts are instrumental in assembling and maintaining vehicles. Yet, these bolts are not classified as sports equipment as understood in the context of the game.