If it’s in an old mausingfield it could be different, since you got a prefit I assume that what know nothing is correct
BARRELS FOR YOUR MAUSINGFIELD
Mausingfield actions with serial numbers of M5A3-00005 through M5A3-00024 use a 1.125” x 20 UN 2B thread, making them compatible with commercially available Savage large shank barrels and locknuts.
Mausingfield actions with serial numbers of M5A4-00025 and higher and all M7's use a 1-1/16” x 20 UN 2B barrel thread, making them compatible with commercially available Savage small shank barrels and locknuts.
Both types of barrels can be easily installed without the need for custom machining. Please note that the 1-1/16” x 16 UN thread of the M700 is not the same as that of either the Mausingfield or the Savage. Therefore, Remington M700 barrels are not compatible with the Mausingfield.
The Mausingfield can also be fitted with threaded and shouldered barrels that do not require a locknut. Such barrels should have a minimum shank diameter of 1.20 inches (30.5 mm), unless they are to be installed on a Mausingfield action having a serial number between M5A3-00005 and M5A3-00024. For actions with any of those numbers, the barrels should have a minimum shank diameter of 1.25 inches (31.7 mm).