How Much Do Crank Bolts Weigh? (Look SRM, THM & SRAM DUB Compared)

Nico had been chasing grams for two seasons — titanium in every derailleur bolt, carbon cages, latex tubes, his bike at 6.85kg. Then he pulled the crank for a BB service. The crank bolt came out with the arm: steel, 15.5g. A single fastener buried inside the spindle he'd never thought about in two years of obsessive weight-weeding.

"That's the thing about crank bolts," Nico told me later, spinning the little steel cylinder between his fingers. "You never see them. You never service them. You install the cranks once and forget they exist until the next BB overhaul, two seasons later. And then you weigh one and realize it's the heaviest single fastener left on the bike."

He'd swapped pulley bolts that saved 3 grams. Limit screws that saved 2. But the crank bolt — the one holding the entire crankset to the spindle — had never crossed his mind. A quick search later and he had numbers. His Look crank bolt, 15.5g of steel, had a titanium counterpart at 11.0g. SRAM DUB riders were looking at 16.1g stock versus 10.5g in titanium. The THM system was already lightweight, the swap being more about material consistency than grams saved.

The torque numbers came up immediately — crank bolts see 35–50 Nm. But the bolt is in tension, not shear. The clamping force draws the arm onto the spindle taper, and the taper carries all the pedaling load. Grade 5 titanium at 900+ MPa handles those numbers without drama. A dab of grease on the threads and under the bolt head, torque to spec, done.

Nico did the swap during that same BB service. Greased the bolt, torqued it down, remounted the cranks. 4.5 grams lighter. He didn't feel it riding — who feels a crank bolt? — but he knew one more steel part was gone from a bike becoming, bolt by bolt, something lighter than stock.

His bike is at 6.845kg now. Not because a crank bolt changed how it rides. Because on a bike built bolt by bolt, the crank bolt was the last place steel was hiding — and now it's not.