High accuracy digital radius gauge Electronic Inside and Outside Radius Gage with 10mm /20mm /30mm /60mm/100mm changeable measuring jaw Black 0.2" - 27.5"/5 mm - 700 mm

This does an excellent job measuring large, partial circle radii. I used it on a couple dozen parts where I needed to measure stuff where nothing else (other than a CMM) would work. I also compared it to regular diameter measurements on a few parts where I could take that type of reading and got good agreement.You need a known straight surface (such as a parallel or a surface plate) to set the zero, and you need to get the indicator perpendicular to it. If you are going to be using it a lot, you might want to 3D print a jig to set the perpendicularity. Make sure you leave enough stroke on the indicator when you zero it; its important to think about where to tighten the set screw on the indicator! If you are measuring a internal radius, you need to zero with the plunger most of the way in. An external radius will need the plunger extended when you zero.Taking measurements is a bit fiddly. You have to seek out two things: getting the span of the bar along the radius you want to measure, and getting the indicator perpendicular to the surface. On the external radius of a cylinder, rotating the whole thing without tipping it will give you a reading that has infinite radius when the bar is parallel to the axis of the cylinder. The minimum radius you read will tell you when the bar is perpendicular to the axis of the cylinder. At that point, tip the indicator back and forth, pivoting on the pair of spheres on the bar. At this point, you want to find the largest radius; this is the actual measurement.Yes, its fiddly to get a measurement! However, I found it very repeatable, and it works where nothing else will! I had a pair of parts with matching inner and outer radii, and the readings I got agreed for the inside and outside.You need to read the chart and pick the right bar; otherwise your accuracy will be worse.Follow the instructions on setting which bar you are using; its easy.

This is a solid product, with the basic capabilities I needed. The foam inside the case is snug, but because the cuts in it are deep, sometimes it can be difficult to get certain accessories out of the case. While the slot depth can be an inconvenience, it isn’t the end of the world, and if you need to measure curves, it does a good job. If you are measuring compound curves or splines, you will have to make multiple measurements. Also, make sure you have a high quality reference surface and stand to zero this out each time, as the larger diameter attachments rely on fairly high precision.

I never even knew someone who used or owned a radius meter, until I needed one, and couldn't find one anywhere. The unit I purchased from Great Wall is a superb precision instrument and helped me tremendously to solve a big problem with a metal bending machine. The unit is so accurate and well built, that it can be used for other measurements as well, such as a very precision depth measuring device, ignoring the calculations that it performs to determine radius. My only wish is that it came with a larger attachment, as measuring the radiusus that I needed is a bit difficult from only a 100 mm (maximum size tool) sample. But that said, it does work and work well. I recommend it and the company. Jim

This functions well. It feels a bit cheap. But for the price I'm happy with it.

Works well and versatile with all the attachments; I'd recommend it!

Works well! Accurately checks radiuses on rolled steel plates. Would buy again.

Perfect for my needs.