A good late 19th century example of The Realm Coin Tester by HELLIWELLS of Sheffield.

Typically attached to shop counters and, according to what we can find online, used to detect counterfeit 'silver' coins by placing them in the slot and applying pressure to see if they would bend.

Steel slots for sixpence, 1 shilling, 2 shillings (a florin) and 2 and sixpence (half crown), early versions of these coins had high silver content.

Screw mounted on an oak backing.

1¹/₂ by 3⁵/₈ inches overall.

Please see images.