Is Perazzi. I had several guns that had them. Think MX3 single barrel was one of them. Possibly my MT6 used it. Not sure of that.
It looks like a early Perazzi type knurling, but the ones I had went full circle and were flat steel. They were with the MT-6 and TMS which were the very early TM-1 with tubes. This one may be an after market wrench. It may have been the MT-6 wrench so it would fit on the o/u barrels between the chokes.
according to their website the Hastings gear choke and the Perazzi type 1 and 2 have the same pattern. they don't list this tool anymore (pity) but their smaller wrenches fit my MT6s. the original perazzi wrench went full circle but was thin to fit between the choke tubes on the O/U bbls.