Seems like all I do here is ask questions!

[Bill Houghton]

I think they sell those female to female extensions in the DIRTY store.

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Now I understand your name...

[Northwoods]

I think they sell those female to female extensions in the DIRTY store.

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Some guys like to check them out, but they really don't want to buy one?

[Chillylulu]

I've got ½" M-M with female ratchet sets, but F-F?  Female square to female hex are used for lug nuts, but tapered rod.   

My guess would be for removing plugs - they mostly have square heads.  I'm thinking steel/cast iron/ malleable iron.  Most brass plugs have hex heads.

1/2"  plug is .56" square, 3/8" is .44" square.

For fire protection our smallest is 1/2" where sprinkler heads thread in.

Double check the dimensions, if both are right at 1/2" I am off on my guess.

Another possibility is a drive shaft as part of an assembly.  I would think that the holes would be longer than needed for a drive tool extension.

Chilly

[Northwoods]

The holes are right at 1/2"---and they are 1 1/4" at the deepest.  Hmmm....

[bill300d]

Sounds like it might be an inline socket wrench.

[Northwoods]

Sounds like it might be an inline socket wrench.

Mine has a round shaft.  So, that doesn't seem likely.   I have some like this:

  http://alloy-artifacts.org/Photos/tools/fairmount_ds1618_wrench_socket_inline_f_cropped_inset.jpg