Sounds like a Lyman combination tang sight.(pat. date Jan. 28, 79 and May 6, 84). The later ones had the Lyman combination tang sight second variation.(improved knurled sleeve)(pat. date July 25, 1905)Base stamped "Lyman Middlefield, Conn. The second are a lot more common and affordable as both have the flip down peep. Code on back underside of base will say "SB" indicating Single Shot .22 and .30-.40 caliber. Discontinued in 1955. Ebay is a very good source if not found here.
HS 58
