Yours has Spanish proof marks and is 6.35mm caliber = .25 ACP! Which works in a revolver because it is semi-rimmed. That got you shooting a "modern" caliber for less than half the price of an automatic.
There are pages and pages of these little pocket revolvers in the old catalogs and the Zhuk reference book. Pinning down an actual manufacturer can be difficult. The FA prefix on the serial number might be a clue. Maybe Francisco Arizmendi, who is said on the velodog www to have been the largest maker in Spain, maybe anywhere.