The markings are quite rubbed but the top of a “u” is easily recognizable in the hallmark under magnification which dates this one to 1835. Its is also stamped S. Mordan & Co. Makers & Patentees along with SMGR; from the period when Mordan and Gabriel Riddle were partners. Very good working condition.6-sided capstone; no chips.
"S. Mordan & Co's. Patent", "SMGR", hallmarks for London, 1835