Class M2 14-Piece Small Calibration Weigh Kit Carbon Steel with Chrome Finish - Red - American Weigh Scales

This set of weights exceeded my expectations for accuracy given the price point. I will be the first to say that the case on this absolutely sucks. The holders for the round weights aren't terrible, but the spots for the square weights below 1g really need to have a better cover. The stock cover for the holders doesn't cover the entire opening. As such, the smaller weights (especially the ones below 100mg) are prone to escaping from their compartment and flying around the case. The bottom part of the case is made from two plastic pieces glued together, but there is a gap between them. When I first put this set of weights away, I didn't know about this problem. When I opened the box the next time, the 1mg weight was mysteriously gone, and some of the other weights were scattered around the inside of the box. Low and behold, the 1mg weight found its way into the very bottom of the box, between the two glued plastic pieces. The only way I was able to retrieve the weight is via the assistance of a strong rare earth magnet (prying the box apart would have worked as well). I suspect this is why some other reviewers are losing their smaller weights.To avoid this happening again in the future, I designed a 3D printed cover that protrudes slightly into each compartment. The OpenSCAD code is at the end of this review. My piece printed slightly tight, so I would recommend scaling down by a few percent if you print this yourself. I'm also not entirely sure if it's necessary to run the cover down into each compartment - a flat cover might be perfectly acceptable.Now for the part of the review I'm sure most came here to see... the actual weight of each of these weights. To weigh these, I used my Mettler Toledo AE 260 scale. It is an older model, over 20 years old at this point, but it's still accurate and precise. There is a built-in 100g calibration weight, but I was worried it might have lost some mass due to corrosion over the years. I ended up buying a 10g ASTM Class 1 calibration weight, and my scale measured this as between 9.9999 and 10.0000grams after calibrating to the internal 100g weight. Essentially: the weights I have measured here are precise to 0.1mg, with the caveat that they are potentially up to 0.1mg less than the true weight, according to an ASTM Class 1 calibrated weight.The theoretical weight, and my measured weights are as follows:50g: 50.0095 g20 - 19.9976 g20 - 20.0016 g10 - 10.0052 g5 - 5.0014 g2 - 1.9983 g2 - 2.0011 g1 - 1.0015 g500mg - 499.9 mg200 - 200.0 mg100 - 100.5 mg50 - 50.0 mg20 - 20.0 mg10 - 10.0 mg1 - 1.1 mgAs you can see, the actual weights are relatively close to the listed weights. They're not perfect, and off by quite a bit when compared to many international standards. That being said, these weights are not meant for high accuracy lab work - they are meant for a home user. Although I'm sure there are some, I'm not presently aware of any home applications where a 10mg error at 50g is a deal-breaker (honestly, this is even perfectly fine for a lot of general lab applications).As long as potential buyers of this weight should are aware of the intended user base, I think this a great set. I personally just use this to verify my scale is reading in the right ballpark across its entire range, and for that it's great. Of course I would prefer a full set of ASTM I calibrated weights with a nice case, but I don't want to spent $500-$1000 on a set of weights.For anyone reading this review, please note that the weights listed above are for my specific set of weights only. I can almost guarantee your set will be different. What you're paying for when you buy an $80 ASTM calibrated weight is the guarantee that it will definitely be within 0.xxx mg of the specified weight. With this cheap set, all you are guaranteed is that the weight will be within a few percent of the specified weight. Some will be nearly perfect, but many will be off considerably.OpenSCAD code for replacement lid:module indentations(){cube([14.5, 20.5, 5]);translate([16.25, 0, 0]) cube([13.5, 20.5, 5]);translate([31.5, 0, 0]) cube([13.5, 20.5, 5]);translate([46.75, 0, 0]) cube([12.5, 20.5, 5]);translate([61, 10.5, 0]) cube([7.75, 10, 5]);translate([70, 10.5, 0]) cube([7, 10, 5]);translate([79, 10.5, 0]) cube([5.75, 10, 5]);translate([86, 10.5, 0]) cube([5.75, 10, 5]);translate([93.5, 10.5, 0]) cube([5.8, 10, 5]);translate([61, 0, 0]) cube([14.5, 8.75, 5]);translate([77.5, 0, 0]) cube([10.1, 8.75, 5]);translate([89.5, 0, 0]) cube([10, 8.75, 5]);}translate([0,1,0]) indentations();translate([0,0,1]) cube([99.5,23.5,5]);translate([25,5,3]) cube([8,12,10]);translate([67,5,3]) cube([8,12,10]);

Good quality and accurate

Awesome value, useless tweezers, sadly missing the 100g weight that would make the kit complete. I bought a 100g weight hoping i could modify the box to fit it into the space that seemingly was made to fit it so that i could have a complete set that I could use to calibrate my new 200g scales. (both of which need 200g but one of which needs both 100g and 200g)I used a razor knife to separate the inner frame from the box, pulled out the inner frame from the box, then i used a forstner bit size 7/8 to drill the bottom out of the 100g spot. The foam in the lid was too tight for the box lit to close w/o distorting it so i used a 5/8 fortner bit turned backwards by hand on the foam to cut a nice circle, using the same trick i cut a circle in a piece of smooth cardboard and pressed down on the foam so the cut circle would 'pop up' through the cardboard and used an extendable razor knife to slice off about 80% of the thickness of the foam; now i have a complete set including 100g individual weight and enough other weights i can easily calibrate my two 200g scales.I managed to 'tiddly wink' one of the 20mg weights across the room and lost it and am pretty sure the kit came with a 5mg weight that went missing on first use; so word to the wise be very careful opening the ziplock bag with the micro weights!My new scales have 0.01g precision and all the weights appear to be well within 0.01g tolerance as i've been getting exactly repeatable measurements.the mg weights could be made better and with consistency (e.g. all stainless steel so they won't disappear in the presence of a magnet) and it would be *really nice* considering the size of them and the negligible cost, that there might be some spares! That said it would be a solid 5 stars if it had the mystery 100g spot filled with a 100g weight and if the tweezer included wasn't pointlessly useless (wouldn't open enough to pick up the 5g weight and broke when trying to stretch it open big enough to do so, also wouldn't grab the mg weights so really literally useless). Super happy on the purchase and would most definitely buy again. (and modify again and through out the useless tweezer again)

First off, Love the kit, used it a few times to check the accuracy of the scales I bought online, it has all the weights to check many scales. used it to calibrate the scales of a few business friends of mine, Great buy and strongly recommend this.Now for the downside, the Case is a POS as it sits. I also purchased the 100 gram weight separately to fill the empty hole. Thought it odd to sell it separate, until I got it home and tried to put it in, I see why, it won't fit. the problem is the cheap molding process, the insert has a 'bottom' for the weight. Now for my fix, for the largest hole 100 gram, got my dremel or any small rotary tool with a small cutting bit on the tip and cut out the 'bottom' or shelf on the insert, careful to Not go thru the outside case.Carefully cut around the outside edge at the bottom of the hole and it will lift out. this is a 2 part case glued together, but they forgot to cut out the insert. This is taking me longer to write it then it took me to do it. The weight fit almost perfect.Only thing left is the foam on the lid, press the lid closed a few moments and see the imprint, cut this out with the rotary tool.All done, Fits pretty good now. Takes about 10 minute to do this job.Now the little cover for the real small weights is not well designed at all, I got a scissors and a bit of Velcro, not too pretty, but it works. The weights are Great, but the case is not. But I still recommends this.

Received promptly. Weights seem to be extremely accurate with exception of 20 and 10mgs. Please note that my scale is by no means professional - "Infiniti" so it could well be my scale. Honestly I do not care as I do not even use such a small weights and generally needed weights to calibrate and verify the scale itself once per a while. Unless you are in pharmaceuticals I would definitely recommend this weight set.

Liked it

Un excelente producto para mantener calibrada tu gramera/báscula y que debes tener sí o sí.El material del que están hechas se siente de buena calidad y su peso es exacto al que se visualiza.

Cumple mis expectativas

nice kit but i got 2x 10mg instead of 2x 20mg. but i got 1mg that is not listed.i tested all the weight with a very precise scale (0,001). only the 50g is not very precise with 50,02g ... all the others are very precises.nice kit and yould recommend it.