I'm a sucker for these marriage commemoratives of Gordian III and Tranquillina. This one has an obverse die break affecting the legend at the 10:00-11:00 position, which is seen in other online examples (below). After an internet search, there appear to have been only a few obverse and reverse dies used to strike this coin. As always, feel welcome to post anything you feel is relevant. Gordian III, with Tranquillina, AD 238-244 Roman provincial Æ Pentassarion; 26.1 mm, 13.33 g, 6:00 Obv: ΑVΤ Κ Μ ΓΟΡΔΙΑΝΟC ΑVΓ CЄ - ΤΡΑΝΚVΛ-ΛЄΙΝΑ, laureate, draped, and cuirassed bust of Gordian III right, vis-à-vis diademed and draped bust of Tranquillina left Rev: ΟΔΗΞ - CЄΙΤΩΝ, Sarapis standing left, extending arm and holding scepter; E (denomination) in left field Refs: AMNG I 1696; Moushmov 1696; Varbanov 4599; SNRIS Odessus 15 (a9). Obverse and reverse die matches to: CNG electronic auction 231, 14 April, 2010, lot 131 Gorny & Mosch, Giessen, auction 247, 10 March, 2017, lot 4261 Wildwinds plate coin
An observation of your reverse along with the die breaks (obverse) there are a lot of similarities on the reverse devices, the softness of the upper part of the T and O look the same, position of the scepter to the C and lettering to the beading seem to match the examples. Are the indentations in both obv. and rev. to keep the coin from moving when minted?
http://www.forumancientcoins.com/dougsmith/pit.html My page on this question dates to a time before I had a digital camera and never got updated. Part of me wants to work on the old pages and part says to work on new projects so I generally do nothing. If you search Coin Talk and the Internet in general you will find many discussions on the matter. Try 'Centration Dimple'. Short answer: These are remnants from tools used to smooth flans before striking.
My example with the Nemesis reverse has the dimple squarely on the poor ladies mouth and a fatal chest shot on the reverse.
Excellent coins. I have a very worn example of a Gordian-Tranquillina type - in fact it is almost unimaginably worn. So here's a Serapis of Postumus.
I am bringing up another Golden Oldie Thread because I was so thrilled to find a @Roman Collector die match to one of my own. Definitely obverse match to the OP, probably reverse too. Mine (with a bunch of attribution stuff I filched from RC - thanks RC ). Note the obverse flan flaw running through the legends at 10 o'clock as noted in the OP: Gordian III Æ Pentassarion (238-244 A.D.) Moesia Inferior, Odessos AVT K M ANT ΓOΡΔIANOC CE(B) TΡANKVΛ|ΛEINA, laureate, draped and cuirassed bust of Gordian right, facing diademed and draped bust of Tranquillina left / OΔHCCEIT[ΩN], Serapis standing left, raising hand and holding sceptre, E in left field. Attribution: RPC VII.2 (unassigned ID 28565); AMNG I 1696; Moushmov 1696; Varbanov 4599; SNRIS Odessus 15 (a9). (10.38 grams / 26 mm) eBay Feb. 2022 Mine and the OP: If I may be so bold, I would suggest a slight tweak to the OP attribution - the obverse flan flaw goes through the ANT part of the obverse legend (which is still visible, just obscured some). The ANT is omitted in the OP attribution. Not in the original thread (because not available in 2017, I presume), I found that RPC Online has this as RPC VII.2, — (unassigned; ID 28565) with 18 examples. I found seven of these are obverse die matches with the obverse flan flaw, several of these are reverse die matches too (some of these were already noted in the OP). https://rpc.ashmus.ox.ac.uk/type/28565 That flawed obverse die apparently had a long life.