I did a story awhile back with a different magazine where I wanted to test the accuracy of a pile of clicker torque wrenches I had collected including two wrenches from Harbor Freight. There is a lot of talk on the internet about the decline in the quality of tools and I thought it would be educational to evaluate the situation. The testing would ignore personal opinion and brand loyalty and just stick with the facts. Over 20 years ago, I contacted a company called Cornerstone Metrology Service and the Director of Quality, Keith Chauvie helped me. Their shop was right across the alleyway from our shop next to the Van Nuys airport so it was really convenient. Their main business is calibrating aircraft and aerospace instruments so I figured they knew what they were doing.

The test we performed was at first intended to compare the accuracy of three different torque wrench manufacturers. But that quickly became less important when Keith suggested that we subject a Harbor Freight torque wrench to a long-term test where the wrench was left at the 70 ft-lb setting for 30, 60, and finally 90 days. After 90 days, the wrench had lost roughly 4.5 ft-lbs of accuracy. In other words, set at 70, it actually recorded a torque average of 65.5 ft-lbs. This was a test Keith performed in 2012. Just a few days ago, Keith called me to tell me the wrench was still sitting on the shelf at his shop and still set at 70 ft-lbs.

He decided to test it again after three and a half years. I thought that it would have lost even more accuracy, but it turns out that after five tests, the average was exactly the same as the results he generated in 2012 – over three years before. So it appears that while our Harbor Freight ½-inch drive torque wrench did lose 4.5 lb-ft of accuracy, it didn’t degrade any further after sitting for three-plus years. I think this says something about the quality of these inexpensive torque wrenches from Harbor Freight. He the recalibrated the wrench and brought it back to me, where it now sits in the torque wrench drawer with my other clicker style wrenches. I think I’ll be using it now since I know it’s calibrated.

When Keith stopped by my shop, the subject quickly led to a discussion about accuracy of measurement and I mentioned I wasn’t sure how accurate my dial bore gauge was after using it for over 20 years. He just so happened to have his 4.00-inch inside diameter standard so we set up the dial bore gauge using a standard fixture he had brought along. We tested my old yet still functioning Peacock dial bore gauge and discovered that it is accurate to within 0.0003-inch, which is more than accurate enough for the ham-fisted engine building that I muddle through.

He also showed me a dial bore gauge setting fixture that he built based on a discussion we had in 2012. Of course, I had to have it since it has to add accuracy. This led to a discussion about using the set of gauge blocks that I could use to calibrate the fixture. He said these gauges were accurate to within 4 to 5 millionths of an inch – at the intended temperature of 68 degrees F. He also told me that this temperature was chosen for several reasons with one being it is close to the average surface temperature of the earth! One block, for example, he said is accurate to 4 millionths of an inch (0.000004-inch) which sounds impressive – especially when he told me that a typical fingerprint is 10 to 11 millionths of an inch thick (0.000010-inch). Yikes.

It was fun talking with Keith and now I’m motivated to re-measure the bearing clearances on two engines that are in need of assembly in the coming weeks. I’ve been through that drill already but now I want to see if my new tool will produce improved accuracy. I’ll admit, I get a little geeky over bearing clearances, but I feel that’s far more socially acceptable than obsessing over the Kardashians.