Where can we find coin dimensions?

[Torak]

When looking at different bullion dealer websites they sometimes quote slightly different coin dimensions. They also often dont give a thickness value. Is there an official place to find these dimensions?

Additionally what is the toletance or variation from these values that we can expect without being worried about having a fake?

[Gildeon]

I use this, very good source, although the thickness is not always mentioned.

https://en.numista.com/

 

[RacerCool]

Also, the various online coin and bullion sellers often have coin dimensions in their "specifications" about the coins they sell.

[HighlandTiger]

33 minutes ago, Gildeon said:

I use this, very good source, although the thickness is not always mentioned.

https://en.numista.com/

 

What he says

[Torak]

Thanks

So what about tolerance? I have a silver 2019 Britannia which is supposed to have a thickness of 3mm.

However when measured, the rim is 3.14mm and the centre is 2.64mm.

[Torak]

I'm assuming the rim is what is measured when thickness is quoted. But there is still a fair bit of difference there, is that normal?

[TonyS]

What are you using to measure coins? I use a vernier calliper, I tried my micrometers but the moving anvil rotation could cause damage.

[Torak]

I've been using a digital calliper

[augur]

4 hours ago, Torak said:

Thanks

So what about tolerance? I have a silver 2019 Britannia which is supposed to have a thickness of 3mm.

However when measured, the rim is 3.14mm and the centre is 2.64mm.

The thickness will vary slightly from design to design and the rim can vary over the coin depending how worn or centred the dies are. Take measurements from different positions of the rim and best use an average. I would say 0.3mm variation is within the tolerance. Diameter on the other hand should be spot on: +/-0.01 -0.05 mm depending on coin (modern bullion or circulation issue.

https://www.royalmintbullion.com/Products/Britannia/Silver/UKB19SS

Dimensions	38.61 mm

[Serendipity]

I don’t know if this will help but I’ve printed out this “Coin Diameter Gauge for U.S. & Foreign Coins” which is important for measuring the size of my coins in order to buy the correct size air-tite capsules. I also strongly recommend that you always buy from reputable dealers who generally mention the diameter and thickness of the coins in their specifications. If you don’t trust their specifications then you could check the specs with the Mints who issued the coins in the first place.

http://www.jpscorner.com/images/Ring_Diameter_Gauge_1.pdf

 

[Torak]

13 hours ago, augur said:

The thickness will vary slightly from design to design and the rim can vary over the coin depending how worn or centred the dies are. Take measurements from different positions of the rim and best use an average. I would say 0.3mm variation is within the tolerance. Diameter on the other hand should be spot on: +/-0.01 -0.05 mm depending on coin (modern bullion or circulation issue.

https://www.royalmintbullion.com/Products/Britannia/Silver/UKB19SS

Dimensions	38.61 mm

The diameter of the brit is measuring at 38.71. This is outside your 0.05 tolerance. It is from the eumint via BYB group order so I'm sure the coin is genuine. I'm just wondering if there is a particular methodology to making these measurements which I'm not quite getting correct. 

What I'm doing to measure diameter is putting it inbetween the calipers. Then tightening calipers so they just touch the coins sides. Then I roll the coin so that the coin centre directly aligns between the caliper edges. This pushes the calipers out a little and I know I've reached that perfect point when the calipers no longer increase their reading. Then I return the to the centre position (as I will have overshot a little to confirm I have reached the maximum reading) where calipers are just touching and push the coin forward and back to see if it is aligned perfectly in that direction. Again, if it is not perfect the calipers will increase a little. Then this is the final reading I get.

Basically I'm trying to get a good understanding of how to identify fakes and being sure of genuine coins by taking accurate measurements and getting used to the acceptable levels of tolerance.

[Torak]

Although I'm happy buying from well known reputable dealers I think it would be a useful skill to have and would increase my peace of mind

[silenceissilver]

My own experience with using a digital calliper is also a bit unsatisfying. I think there are two tolerances you need to take into account, one for variations in the actual coins and one for the measurement process. I have to say though I have never tried it with one ounce gold coins, only with Sovereigns and silver coins. There was one half Sovereign I thought was OK after measuring it with a calliper but I got highly suspicious after a specific density test and finally had it X-rayed and it turned out to be 18K instead of 22.

I know, it's in German but at least you can see how one of Germany's big dealers measures coins - and also fakes - the video is actually called “very good fake gold coins”. So the fakes are very close in size. You can also see how the measurements on his calliper jump about a bit, if I remember that correctly.

Edit: When I say I thought the fake half Sovereign was OK after having it measured with a calliper, I actually mean that I noticed that all the measurements, also that of other coins, where not that precise and thus I thought, probably it is alright – but I was not sure.

 

 

[augur]

8 hours ago, Torak said:

The diameter of the brit is measuring at 38.71. This is outside your 0.05 tolerance. It is from the eumint via BYB group order so I'm sure the coin is genuine. I'm just wondering if there is a particular methodology to making these measurements which I'm not quite getting correct. 

I am sure your Brit is genuine but if you just hold the coin as in the video and clamp down and repeat to clamp down after rotating some 30 degrees you should get the given dimension within the tolerances. I haven't measured my silver unless from eBay but I'm pretty sure the Royal Mint is very exact.

[Torak]

Thanks for the guidance guys, really appreciate it. I'll do more measurements as in the video tomorrow.

[silenceissilver]

55 minutes ago, Torak said:

Thanks for the guidance guys, really appreciate it. I'll do more measurements as in the video tomorrow.

The good thing is, if your dimension measurements are not conclusive, the magnet test will bring clarity. I do this now with all my new gold coins (in the past I didn't know how to apply it correctly to such a small coin as a half Sovereign): Two small neodymium magnets that are holding a thread between them. (You can also take one magnet bind it to the thread). You hold the top of the string with the magnet(s) hanging down and carefully bring it close to the gold coin. If it is gold, it will get slightly drawn to the coin. If the dimension measurements are close but the magnet is slightly pushed away, there is tungsten inside.

There are also youtube videos about this with slightly varying set ups. (Bigger neoymium magnet and the coin on a thread; sliding the magnet down the coin etc). Also try it with modern copper plated steel pennies - they will be drawn to the magnet in an uncomparibly stronger way from miles away, so to speak - just that you get the comparision. Gold is diamagnetic, Tungsten (wich has alomst the same density as gold and is thus used in the fakes in this video) is paramagnetic.

This works for me for all gold coins but proof sovereigns in Royal Mint capsules - these capsules are too thick and the coin is too far away from the magnet. Also, what I see with some coins, rather than the coins and the magnet moving towards each other (the effect is not that strong and if the thread is not completely still in your hand, you can miss it), the gold coin moves the magnet with it a bit, when you carefully move the gold coin away a tiny bit, after you brought them together neck to neck, so to speak.

 

Edit: For Silver coins it's even easier, you just let the magnet slide down the coin and you will see it's sliding quite slowly, compared to what you would expect at a certain angle. Sometimes, with one ounce gold coins, you can also see the slow sliding effect but it can also be so small that you hardly notice it (with smaller coins sliding, doesn't work).

[Frost]

For me the most truthworthy resoures are official mints' websites

[Torak]

Ok I'm getting 38.67 now which is closer. If I apply a decent amount of pressure I can get it to 38.63 but after I release the pressure it jumps back up. The specified diameter is 38.61.

 

@augur out of interest why do you allow a larger tolerance for coin thickness?

[PansPurse]

I feel you might be worrying slightly overmuch about tiny differences in diameter. Checking weight and specific gravity is more helpful for making sure it's the correct metal. The fakes I've encountered have all had pretty significant discrepancies between their dimensions, weight, appearance etc. Also if it's a silver Brit then bear in mind that the tolerances will inevitably be a little larger than for gold (getting a little more than an ounce of silver in the coin is pretty standard). I don't think there's much interest in faking modern bullion britannias (although I may be wrong). I suspect your coin is fine, but a specific gravity test should confirm it.

[Torak]

@silenceissilver

I've just ordered some neodymium magnets so am looking forward to playing around with those.

Now this probably deserves it's own topic but I'll post it here for now...

My understanding is that diamagnetic materials weakly repel magnets and paramagnetic materials weakly attract magnets. So I'm not sure why the gold should be attracted to the magnet in your test, as it is diamagnetic.

With the case of a changing magnetic field (in the slide test it is changing because it is moving) this causes eddy currents which produce magnetic fields which oppose this change. This explains the drag seen with silver. Different metals due to properties like conductivity will have this effect to varying degrees. Obviously ferromagnetic metals will simply stick together. I'm not sure why silver has such a strong effect and gold such a weak effect. Silver is more conducting than gold but not hugely. Still I understand the principle.

I realise this is quite technical, but I'm just interested to know if anyone would know anything more about this. No worries if not, this is something I wish I'd bought up with my lecturers back in uni days!

[Torak]

@PansPurse thanks. Tbh I'm not really worried about it being fake, I'm just trying to get used to measuring and understanding what is an acceptable difference.

That's good to know about the occasional slight increase in weight for silver coins.

Yeah I will be doing a specific gravity test at some point. Again not because I'm paticularly worried but just because I want to get some experience and have some fun with it!

[PansPurse]

3 minutes ago, Torak said:

@PansPurse thanks. Tbh I'm not really worried about it being fake, I'm just trying to get used to measuring and understanding what is an acceptable difference.

That's good to know about the occasional slight increase in weight for silver coins.

Yeah I will be doing a specific gravity test at some point. Again not because I'm paticularly worried but just because I want to get some experience and have some fun with it!

Sounds like a good approach. It's worth taking a little time on as an education to help you spot problems in the future 😌

[silenceissilver]

24 minutes ago, Torak said:

@silenceissilver

I've just ordered some neodymium magnets so am looking forward to playing around with those.

Now this probably deserves it's own topic but I'll post it here for now...

My understanding is that diamagnetic materials weakly repel magnets and paramagnetic materials weakly attract magnets. So I'm not sure why the gold should be attracted to the magnet in your test, as it is diamagnetic.

With the case of a changing magnetic field (in the slide test it is changing because it is moving) this causes eddy currents which produce magnetic fields which oppose this change. This explains the drag seen with silver. Different metals due to properties like conductivity will have this effect to varying degrees. Obviously ferromagnetic metals will simply stick together. I'm not sure why silver has such a strong effect and gold such a weak effect. Silver is more conducting than gold but not hugely. Still I understand the principle.

I realise this is quite technical, but I'm just interested to know if anyone would know anything more about this. No worries if not, this is something I wish I'd bought up with my lecturers back in uni days!

You are actually right. I think my setup doesn't work or I didn't carry it out carefully enough. The effect with my little magnet is so small that I interpreted it as the gold being attracted and knowing it's from different very reputable sources I then thought that's what it should be despite knowing it better. Intriguing what little tricks the psyche can undergo. I think I have confirmed the Milgram experiment, involutnarily. Not me, usually. I will order a bigger magnet and work on my set up.

[silenceissilver]

Or all my gold is fake 😲 Thanks God, my Sigma Metalytics Pro will arrive soon

 

 

[Torak]

Haha I'm sure you're good! The effect is very small, so even if you caught a small movement you probably just assumed it was in the direction you expected!