I buy a few thousand dollars in parts from Midway each year, but they’re not great for this kind of resto-repair. They’re great if you’re doing basic work or building an AR or 10/22, but Midway gave up 10yrs ago or more on really supporting gunsmithing efforts, and they aren’t a warehouser for obscure or obsolete take-off parts, which haven’t been made in ~3/4 century.

It hasn’t been made for 75yrs, and this particular part is notorious for breaking - they sell out quickly when they come available, aka, when someone gives up a rifle to a gun buyback and a parts reseller finally has access to them. Lots of folks waiting for them, and not many available.

No, that’s the Extractor plunger, a component of the bolt. The EJECTOR plunger assembly in the 121 mounts in the rear of the trigger guard, basically a spring loaded buffer which pushes the firing pin forward to act as an ejector. Novel idea, but less than ideal, and less than ideally executed. The ejector plunger assy has thin mounting flange around the tubular body through which a retaining screw fixes it to the receiver - but this flange is prone to breaking, such replacements are exceptionally difficult to find.

The repair is pretty simple - longer retaining screw and a notched washer, reamed to fit the housing. But it’s not factory original...