Bolt Length Calculator Online (Through-Bolt & Tapped-Hole Joints)

bolt Length Calculator (Through-Bolt and Tapped-Hole Joints)

A bolt that is too short lacks thread engagement and loosens; too long it bottoms out, looks sloppy and may foul adjacent parts. The online calculator on this page works out the theoretical required length from joint type, clamped thickness and washer set, then rounds up to the standard length series - ready for purchasing.

Length builds up as L = clamped thickness b + engagement (or nut) + washers + 1~2 exposed threads. For through bolts with a nut: nut height (about 0.8d, using actual GB nut values) plus about 0.15d exposure. For bolts threaded into a tapped hole, engagement by material: 1d in steel, 1.5d in cast iron, 2d in aluminum (softer material needs more engagement). Washers add about 0.25d for a spring washer plus the actual flat washer thickness.

Take clamped thickness after compression for gaskets or flanges, and add for countersinks or inclined seats. Pair with our weight calculator for bulk purchasing. Zhuhai Jiali Hardware manufactures precision screws and custom-length bolts - contact us for quotes.