My point is that you don't make the rules when it comes to tack terminology. Language develops from popular usage. With the exception of technical (scientific) terminology, language is "by the people and for the people." Definitions come from general consensus. If tack stores, and the bit maker, and educated trainers all call the OP's bit a Tom Thumb--and they do--then by jove it is
a Tom Thumb. Because Tom Thumb is just a name, and not a definition. You can argue that it's not the same as the bit I posted, because it's not, really, having some variation in the shanks....but both will still fall into the general consensus Tom Thumb category. Because that's how people--the majority of people, not one individual, who has not, by the way, authored Webster's--defined them. tom thumb bit - Google Search
^ Unless everyone
else is wrong and you (by the power and authority granted by....whom?) have somehow made some edict to the contrary.