Sometimes the same type of ancient coin comes in different sizes. This is especially common in the Byzantine series which is not noted for its quality control. Here are two coins of Leo V and Constantine (with "Λ" for Leo and "K" for Constantine): Leo V and Constantine, 813-820, struck at Syracuse. Left coin: 22-20 mm. 2.67 grams. Right coin: 18-17 mm. 3.28 grams. Heavier! Sear 1635. DOC 3.1 19. INC 2015 Proceedings (p. 991) had an article arguing this is really Leo IV and Constantine VI. I found the argument strong, but I give the Sear and DOC citations anyway. Show us two coins of the same type and denomination that are not the same size!
That's a good idea for a thread. I wish I had the large module one. This is the small module issue. The coins of 685-720 would have a lot of examples. Or the 260s.. GALLIENUS AE sestertius. Joint reign, first emission, struck circa 253-254 AD. IMP C P LIC GALLIENVS AVG, laureate cuirassed bust right. Reverse - VIRTVS AVGG S-C, Soldier standing left holding spear and resting left hand on shield. RIC 248, Cohen 1295. 27.5mm, 15.7g. Small module 81642. Orichalcum sestertius, RIC V 216, C -, aVF/F, 12.464g, 25.2mm, 180o, Rome mint, [IMP C P LIC GALLI]ENVS AVG, laureate and draped bust right; reverse [IOV]I CONSERVATORI S C, Jupiter standing left, thunderbolt in right, scepter in left; exceptional portrait, typical tight chunky flan; The Sestertii of Postumus would also yield good examples.
Here are two Byzantine coins of Constantine VII, 913-959, struck c. 945-950 at Constantinople: The one on the left is larger than normal. It is 31-29 mm and 10.55 grams. The one on the right is normal-sized--26-25 mm and 9.22 grams. Sear 1761. Most (all?) coins of this type are overstruck on previous coins, so the flan size depends upon which coins were used as flans. Many undertypes are of Romanus I, but neither of these has a clear undertype. There are other Byzantine types which come in various sizes, even though the denomination is the same. Are there Greek or Roman examples?