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Jennings / JScale Mack 20 Digital Precision Scale

Innovative dual display design.
20 gram capacity x 0.002 gram resolution

"In A Nutshell"
PowerAC adapter (not included)
4 AA (included)
DisplayBlue backlit LCD
Tare FeatureYes
Calibration FeatureYes
Platform Size1.5" diameter
Scale Size7.0" x 6.5" x 2.5"
Weighing Modes8

Included Accessories

  • 7.7" x 7.0" VibraKill® Pad
  • 20 Gram Calibration Weight
  • Expansion Tray
  • Four AAA Batteries

Weighing Modes

Mode: GramsCapacity:20.000 gResolution:0.002 g
Mode: GrainsCapacity:308.60 gnResolution:0.02 gn
Mode: Troy OuncesCapacity:0.6430 oztResolution:0.0001 ozt
Mode: OuncesCapacity:0.7050 ozResolution:0.0001 oz
Mode: PennyweightsCapacity:12.860 dwtResolution:0.002 dwt
Mode: CaratsCapacity:100.00 ctResolution:0.01 ct
Mode: TicalsCapacity:1.1700 t mgResolution:0.0002 t
Mode: MilligramsCapacity:20,000 mgResolution:2 mg

Product Details

Two Weight Displays?That's right. Jennings designed this jewelry scale with two, bright blue, LCD weight on the front, and one on the back. So whether you load the scale from the front or the back, you won't have a problem seeing your weights.

Auto-Off FeatureIf ya have ever had the batteries in something run out because you forgot to turn it off, you'll realize what a blessing this feature is. The Mack-20 will automatically turn off after a few moments of inactivity, saving battery power and money.

Bright Backlit DisplayThis digital scale has a fancy, blue, backlit display to help ya see your weight readings, even in dim lighting.

Hinged Protective WindscreenWhen you're weighing with high precision scales like this one, even the tiniest breeze can interfere with weight readings. This Jennings scale comes with an attached windscreen to keep out those pesky drafts. The protective cover is hinged, just press the button on the side to release it and lift it out of the way.

It Remembers The Last Unit Ya UsedIf your application needs weights in the same unit of measurement, (like ounces for instance), it can be a real pain if your scale always turns on ready to weigh in grams. It's a good thing the Mack turns on displaying the unit of measurement you were using when ya turned it off.

It Has WeighMeter™ Technology!If ya put too much weight, (more than the capacity of the scale) on any scale it can cause permanent damage. Unfortunately, most scales warn ya of an overload after it's too late. Luckily this digital scale comes with WeighMeter Technology to tell ya when you're coming close to the maximum capacity. This will save ya from overloading your scale and damaging it beyond repair.

Easy CalibrationTo make sure ya keep getting the best weight readings from your scale, it helps to calibrate it from time to time. This jewelry scale has instructions to make calibrating your scale easy. The Mack even comes with the 20 gram calibration weight ya need to use.

Tare FeatureThe tare button on the front of this digital scale can be pressed to "zero out" the weight on the scale. You can then add more weight, and the display will only show the weight of the items you're adding. This sure is useful when ya want to use the included expansion tray to weigh your things, or if ya want to get separate weights of multiple items.

Liquid Level Indicator And Leveling FeetThis very handy feature helps you quickly and easily get your scale nice and level. Adjust the scales foot pads by screwing them in or out until the bubble in the liquid level indicator is centered, and you're off to the races. A level scale is so important for getting the most accurate weight readings.

Four Useful AccessoriesThe Mack 20 comes with great accessories. Use the VibraKill® Pad under the Mack to keep vibrations from messing up your weight readings, and the calibration weight to keep it nice and accurate. If you're looking to use the Mack as a diamond scale or carat scale, the little expansion bowl is perfect for weighing those teeny tiny jewelry pieces. You'll even get a set of batteries so ya can start weighing as soon as ya get it.

Kill Those Vibrations With VibraKill®Did ya know that vibrations can cause a scale's reading to bounce around from one weight to another? Included with this digital scale is a VibraKill® Pad to keep vibrations, (caused by everyday items like, your fridge, nearby music, your washing machine, etc...) from messing up your weighing.

20 YEAR MANUFACTURER'S WARRANTY!If ya have a problem with this scale, just send it to Jennings' warranty center in Phoenix, Arizona. They'll fix or replace your scale and send it on its way back to ya within a week of receiving it. You should expect your replacement to arrive in about two to three weeks from the day you send the original off. Keep in mind that sometimes Jennings runs out of stock, which can cause a delay in the warranty replacement process.

Product Reviews

Overall Customer Rating:
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from 14 customer reviews.
Two bad scales
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Bought the Mack 20 scale for my son to use. First one received was very unstable and would not ever zero, but numbers would drift. Tare or calibration did not help with drifting problem. A second scale, to replace the first one, was received and the display on showed "Error". Pressing any button did nothing or unplugging and plugging back in with the AC adapter did not help. Constant "Error" message displayed. Quality assurance on this scale is very questionable.
Reviewed by: John from Georgia on 6/24/2015
Mack 20 Scale is fantastic
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It wolds zero/tare like a rock. It took a few minutes of searching to find the calibration weight, but it eventually turned up taped to the egg-crate shipping cap. How diabolical. Good thing because it DID require calibration which went without any surprises. I am using this scale to weigh smokeless gun powder and now I can be as obsessive as I want about precision and repeatability. For you reloaders out there, it trickles just fine after a 5 second pause and then becomes stable. It will sense the weight of a single granule of Bullseye. Don't be in a hurry. Try it, you will love it. Can't be beat for the price (get the optional AC adapter).
Reviewed by: Jeffrey Wolf from Menifee, CA on 11/29/2014
Jennings Mack 20
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Couldn't get exact measurements in grains . It goes from 5.98 to 6.02 and it seems it never display an odd number in the hundredths position. Example would be .01, 03 or .05. I do like the scale so I use the scale for the raw measurement then transfer to a different scale to do the minute measuring. The first set of batteries did not last as long as I thought they should. It might have been better if I selected a different scale......
Reviewed by: Gary Heydt from N.E.PA on 10/29/2014
jennings mac 20
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my order arrived on time and in good working order. Old will knott was attentive to the order and I am happy with the function of the scale, wish it had a little more weight capacity at its fine resolution. thanks for your quality service.
Reviewed by: Chris from washington on 5/28/2013
Jennings / JScale Mack 20 Digital Precision Scale
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I needed to measure small amounts of technical epoxies. I use small plastic drinking cups for meter and mix. The cups very a tiny amount in weight. The scale tare is great for this and gives me the accuracy for mix I need. I wish it had rubber feet otherwise a great scale design.
Reviewed by: Lee Zuhars from Seattle on 3/17/2013
Jennings Mack 20 Scale
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Scale is working fine after 1 year, is well built. Dual displays is a nice feature even though I'm not using it. Is it really precise to 0.002 grams? No. I don't think that anything short of a true high-end scale can do that.
Reviewed by: Joseph Helfand from Ann Arbor, MI on 2/5/2013
Over all good scale
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This is a great scale. kinda jumpy at times but overall usable for what im using it for. It jumps a few hundreds of a grain here and there but not enough to make a really big difference. Also a big thanks to the great customer service i have received from here. Ffirst i received a faulty scale, but with some help from customer service it was quickly resolved and a new scale was on its way in no time. A+++ Highly recommend buying from here weather its the mack 20 or some other scale, old will knott will not disappoint.
Reviewed by: Tou Yang from Fresno, CA on 1/22/2013
a fine scale for the handloader
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one of the best values in a digital scale for measuring powder for hand loading firearm cartridges. easy to set up and calibrate, extremely accurate - i tested it against my other beam and digital scales with know grain weights - and just a good bang for the buck. as with most scales that come with plastic measures, they can be very static prone and sometimes it's best to use a desensitised metal measure.
Reviewed by: rfd from nor'east on 8/29/2012
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After working with my scales for a few days I noticed something was not quite right. I made a phone call to old will's and spoke with one of there tec.'s. We worked on getting the scales recalabrated but with no luck. The tec. worked with me a little more and decided the scales were faulty. Once they decide they were faulty they replace my scales with no problems at all. The tec.'s at Old Will Knott's are very pleasant folks to work with. I would order from them agin.
Reviewed by: William from Kentucky on 8/2/2012
Jennings MACK 20 Scale Review
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I purchased a new Jennings Mack 20 from Old Will Knott Scale Co. and it required recalibrating every time you turn it on and off. Service sent me another unit promptly and it works just fine. Only complaint is the plastic laddle that sits on top of the scale. It has a tendency to statically charge my gun powder particles and stick to the laddle. Service from Old Will Knott Scales was outstanding. Scale works fine for measuring gun powder. It's a winner for the price.
Reviewed by: Victor H from St. Louis, MO on 7/6/2012
Nice Little Scale
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Using this for a powder scale. Nice little set up, seems to be accurate judging by the known weight items we have put on it. Good unit for this price range.
Reviewed by: Les from New York on 6/27/2012
Not very accurate or stable
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I purchased one of these - and it will be going back. I ordered this one in hopes that it would perform to what is described. In short it does not. It came "calibrated" from the factory but it drifts - especially in TARE mode and won't really settle on a weight. An example: (I measure everything in grains btw). Turn the unit on and let it settle to zero. Put the pan on the scale and hit the TARE button and let it zero. A few seconds later it will change it's mind to the tune of a full thenth of a grain or so. When it does zero, put something in the pan and weight it. It seems like half of the time it will not settle on a weight either (44.36gn/44.38/44.42). Pull the pan off and half the time the read out will be a negative number like .16gn. So what ever you weighted can't be trusted. It is supposed to have a .02 grain resolution but it's barely good to the tenth if that. One should not have to chase a zero or a TARE. Recalibration on a level stable surface gives the same results.
Reviewed by: S Allen from Maryland on 5/28/2012
Great Scale!
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I bought this scale to weigh small amounts of weight that I need to add to custom built golf clubs. The weight is either a screw-in, lead tape, or tungsten powder added down the shaft of the golf club; to make it have the correct swingweight and M.O.I. (moment of inertia). The first scale that I received didn't work right. It wouldn't power up? I called to order a replacement, and was promptly taken care of. The replacement scale arived in four days, and works perfectly! I highly recommend this company!
Reviewed by: Stephen Moxley from San Diego, Ca. on 4/3/2012
Jennings Mack 20
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I was looking for a scale to measure gunpowder that was accurate and without breaking the bank. I called and spoke with customer rep Allison who was most helpful and she directed me to the Mack 20. I also purchased the optional AC power adapter. I rcvd it in the mail a few days later and that night I used it with no problems. The next evening I reloaded more rifle rounds and found the scale would not calibrate. A call to OldWillKnott customer service the next day had me another scale on the way at no charge. The first scale was defective . I have now used the scale several times since and I can measure to 1/10th of a grain and repeat the same with no drift in measurements. This to me is important since I am using gunpowder and do not want to see different random measures. I am currently using the scale with 4AA batteries and like the auto shutoff feature if I forget to turn the unit off maually. So far I have been really pleased with my scale. Customer service here deserves 2 thumbs up too. Good job everyone! Thanks from a pleased customer. John
Reviewed by: John from Alabama on 3/28/2012

Product Questions

Number of questions: 0

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