FBI Super Security Hidden Keyway made by Harrington & Richardson Arms.
These are the 2nd model which as an added security measure were manufactured with a milled groove on the side of the handcuff's bows. This was designed to prevent "spreading" the cuffs apart.

These handcuffs patented in 1934 and used exclusively for the FBI are the strongest handcuffs ever manufactured and when in place on the wrist are designed that the keyway is hidden from sight and entrance blocked.

The cuffs are in very good working condition and come with a key.
They retain approx 60% original nickel plating
The cuffs reflect a red background which is in the picture only, it is not on the cuffs!

Please see pics for more info.