1920 UK 3d - how do you tell the difference between Sp#4015 and Sp#4026

The catalogue contains two different versions of the UK 3 pence coin but both versions have a 1920 coin. How do you tell the difference because they seem identical to me? I realise the silver content is different but wanted to confirm whether they are otherwise identical and thus impossible to differentiate

https://en.numista.com/catalogue/pieces21182.html

https://en.numista.com/catalogue/pieces2788.html

If you look closely at the details, you'll see that the 2nd issue is very slightly thicker (to accommodate the change in composition). There is also a difference in the sound they make. The .925 would sound like a 1919 and the .050 would sound like a 1921. Other than x-ray fluorescence to get the exact composition these are probably your best bet for differentiating them.

Good luck!

thanks I hadn't noticed the difference in thickness