This is a Hi-Viz Sight known as the Interchangeable, model HRB2007.
HIVIZ(R) interchangeable Front Sight for Ruger Mark I" II" III and IV steel bull barrel pistols. Also fits: Ruger 22/45 with adjustable rear sight (does not fit the 22/45 LITE); Ruger Single-Six revolvers with adjustable rear sight; Browning Buck Mark pistols (does not fit the Challenge" 5.5 Target" and 5.5 Field). Includes six LitePipes in Green" Red and White.
Features:
Includes six interchangeable LitePipes in red green and white;Front sight