NHRA - National Hot Rod Association

NHRA Expertise: Torque wrench life hack for hard-to-reach bolts

Can’t fit a torque wrench between your engine’s oil pan and flexplate? Use a box-end wrench to extend the reach of your torque wrench.
07 May 2020
David Kennedy
Racing Technology
Torque wrench life hack

Here’s what you need:

  • 3/8-inch drive torque wrench
  • 12-point combination wrench with ½-inch wrench on one side and 7/16-inch wrench on the other
  • This formula: M1 = M2 x L1 / L2

This torque hack works if you slide the 12-point-end of a 7/16-inch box-end wrench over the 3/8-inch-squaredrive of a torque wrench. We used this trick to tighten six flexplate bolts to 35 ft-lbs. using the ½-inch side of the wrench. Technically, the ARP bolts we used have 13mm heads, but the ½-inch wrench fit tight enough. Remember, this is a life hack, we’ve given you links below to the proper tools for this job.

Using the formula M1 = M2 x L1 / L2, where: M1 is the torque setting of the wrench, M2 is the actual torque applied to the nut, L1 is the normal length of the wrench, and L2 is the extended length of the wrench—we found that using our 18 ½-inch long torque wrench with our 7 ½-inch long box-end wrench meant that we’d set the torque wrench to approximately 25 ft-lbs. to torque the bolts to 35 ft-lbs.

Here’s how we worked that out:

  • M2=Torque we want for the bolt: 35 ft-lbs.
  • L1= Length of torque wrench: 18 ½ inches
  • L2= Length of torque wrench + length of extender (7 ½-inch box-end wrench): 26 inches
  • M1=Torque setting we needed for the wrench: 25 ft-lbs.
  • Formula: 25 ft-lbs. = 35 ft-lbs. x 18 ½ inches / 26 inches

Want to use the right tool for this job?

Here are the proper tools for this job from your favorite tool suppliers:

Cornwell Tools Torque Adapter

Mac Tools Torque Adapter

Matco Tools Torque Adapter

Snap-On Torque Adapter

Other torque wrench accessories to check out