If the target torque TA is doubled to 70 in-lbs with L = 8 inches and E = 2 inches reverse extension, what TW is required?

If the target torque TA is doubled to 70 in-lbs with L = 8 inches and E = 2 inches reverse extension, what TW is required?

• A. 93.3 in-lbs
• B. 70 in-lbs
• C. 84 in-lbs
• D. 112 in-lbs

Answer: (A)

When a reverse extension is used, the effective lever length becomes L − E. The torque delivered at the fastener is the wrench reading times the ratio (L − E)/L, so to reach the target torque TA you solve TW = TA × L / (L − E). Plugging in L = 8 inches, E = 2 inches, TA = 70 inch-pounds: TW = 70 × 8 / (8 − 2) = 560 / 6 ≈ 93.3 in-lbs. So set the wrench to about 93.3 in-lbs to achieve 70 in-lbs at the fastener with a reverse extension. (If it were a normal inline extension, you’d use the denominator L + E and get a different value, explaining why the reverse extension changes the required reading.)

When a reverse extension is used, the effective lever length becomes L − E. The torque delivered at the fastener is the wrench reading times the ratio (L − E)/L, so to reach the target torque TA you solve TW = TA × L / (L − E).

Plugging in L = 8 inches, E = 2 inches, TA = 70 inch-pounds:

TW = 70 × 8 / (8 − 2) = 560 / 6 ≈ 93.3 in-lbs.

So set the wrench to about 93.3 in-lbs to achieve 70 in-lbs at the fastener with a reverse extension. (If it were a normal inline extension, you’d use the denominator L + E and get a different value, explaining why the reverse extension changes the required reading.)