Digital torque adapters minimum setting

Question

I'm considering purchasing a digital torque adapter, so I can measure torque with my current ratchet wrenches. I find it curious that almost all the adapters have a minimum setting of around the 20 ft/lbs; only a few start about 10 ft/lbs. At least that's what their listings say on Amazon, however, seeing the package labels, they don't talk about the minimum but the maximum, for example: Performance Tools M206 says 150 ft/lbs. max.

The engine I'm rebuilding has torque settings ranging from 18 to 88 ft/lbs. So a 10-150 wrench will suffice... but what about 10-150 torque adapters? I don't get why a digital device like those, can't read from zero up to the max. 0-150 instead of 20-150?

Answer 1

The reason of why the range is limited may be because those sensors do not have a linear response and accuracy will decrease sharply below and above the declared range. Mechanical torque wrenches have the same problem and are inaccurate at lower ends. As a general rule you can build a precise sensor over a small range, or a sensor with a large range and a lower precision. Also I would not trust a torque wrench declaring a range from 10nm to 150nm unless of a very reputable brand that provide specs. I would suggest you to use a couple different wrenches (eg. 1-10/10-40/40-150).