Overall length 3 inches; diameter at the neck .58. Dorsey and Shaffer show two tompions they theorize are for the Colt Special Model .58 Cal. rifle musket on pages 281 and 281 of vol. 2 of Gun Tools. According to them, the first measures 3 1/16 inches overall and the second measures 2 61/64 inches. In my book (so to speak) that adds up to a 3 inch long tompion as being turned out by the dozen on a wood lathe. In any case, their first example has a fully rounded head like this one. The second has a single slot and flat top, but they note it has a "dimple" lathe mark on the lower end. This one shows such a mark and also one on the center top. At the very least it rates as a commercial .58 Cal. tompion. I leave it up to you whether you buy into the Colt connection.