Any ideas on this one. Marked SKF and 2 15/16. No other markings I can see.

It looks like what I've always heard called a spanner wrench.  I've seen them used in an industrial setting (e.g. removing filter caps, loosely fitting line caps with truck loading/unloading in double block-n-bleed configurations, and gaining access to explosion proof enclosures).

AKA Hook spanner

They are also used for installing and removing certain types of captured bearings, and SKF has been making bearings since before there were automobiles...

It kinda looks like something that came with a repair kit, but I dunno what....

Also looks like the spanner in motorcycle kits to adjust rear shocks, but SKF is a bearing maker.

It is a spanner to adjust a "bearing nut", which is a basically a thin nut with a round Outside Diameter that has a series of slots cut across for the hook of the spanner to engage.  The curve of the spanner matches the OD of the nut.

The spanner doesn't have to apply a lot of torque, as the nut normally is used to hold the shaft from moving endwise in the bearing bore.  The nut is locked by a washer that has a tab that engages a keyway in the shaft and has tabs around the outside.  One of the outside tabs is bent over to engage in one of the slots that the spanner hooks into to lock the nut.

Spanner is just British for wrench.  Anybody remember John Lennon's book, A Spaniard in the Works?  It's a play on words -- throwing a wrench in the works.

Provincial got it right that is an SKF bearing wrench, Quite common in industrial plants but the usually get misplaced and you end up using a punch or chisel to lock or unlock the bearing