Neiko Stainless Steel Digital Caliper (0-6") Expired

I've had one of this exact model for ~2 years and it's surprisingly good. I also went on a little mini-binge during the AliExpress 11.11 sale and bought a bunch of other sub-$20 calipers and find myself going back the Neikos because of the smoother action and light weight. Reading through the comments, here's some info people are asking about.

1) Batteries

They DO eat batteries. The display turns on when the jaws are moved, but since it's reading out to hundredths of a millimeter, it effectively turns on whenever it's bumped and the lock screw isn't tightened. Expect a couple months max, but you can get the LR44 batteries super cheap ($8 for 50).

There are 3D printable models to convert these to take AAA and AA battery. I've printed 3-4 variations and the less bulky ones work very well. Wiring is actually kinda annoying because all the models use some for of removable dummy battery. It's easier to just snip a little passthrough between the battery compartment and dummy battery area, and then solder the wires inside the caliper. Disassembly is easy.

The battery door is the worst part. It WILL fall off or break, eventually. The rails that the door slides along are super thin and there's very little room to MacGuyver a replacement without compromising measuring along one dimension.

The smaller door at the top has data pins, but I've heard that function isn't wired in. The pads are there, though, so it might be possible to go that route for power cables.

2) The other knock offs on ALI/AMZ/TMU

From what I can tell, there are ~10 different sub-$20 models that are rebranded (including the Neiko). The Neiko feels much smoother than the 5-ish other knock offs I have. The super cheap calipers that are easy to mistake for this model don't have the adjustment wheel and are usually fully plastic, but otherwise the exact same boards and body. I got one anyways because I thought it might be nice to have a non-conductive one on hand. If you want to get the same model as the Neikos, just note the button colors/placement, the thumbwheel, and material (metal jaws and slide, plastic housing).

The differences in general are: Metal vs plastic ruler section, metal vs plastic electronics housing, metal vs plastic jaws, display size, adjustment wheel, tenths vs hundredths precision, batteries/case included vs bare tool, battery door sliding vs screwed shut, and length. I think there are 2 variations of the plastic electronics housing and ~3 variations of the metal housing. If you're gonna print a battery adapter, make sure you match up the housing. The slide/ruler dimensions are all the same.

Oh, and the metal electronics housing versions seem like a good idea, but the finish and fitment of the 2 I have is pretty bad. Very scrape-y feeling, like they didn't debur any part. They also weight 4x as much as the Neikos.

Once you break the ~$20 mark on AliExpress, you'll find the same variations with waterproofing and/or backlighting, but otherwise identical, up to ~$35. At the upper end of that range you start to see active data pins (though, apparently, some cheap ones have the data transfer feature enabled).

3) Accuracy

I don't have anything to compare these to, as far as high end calipers. The YouTube channel "bigclivedotcom" did a teardown and explanation of the mechanism used and seemed to be rather impressed. (He disassembles, draws out schematics, and explains the operation of all sorts of cheapo electronics.) All I can say is that when going between these calipers to printing stuff that was measured, I've had zero problems.

If there are any other questions, feel free to post em. I hope that helps someone.

To anyone who's purchasing this, remember to tighten the top screw when you done using it. The caliper will auto turn on when the scale moves, the top screw will lock it in place.

Math is hard.