Grant, this Laser will fit the Ruger Security 9's Rail no issue. Pictured installed here : google.com/search?q=Streamlight+TLR4+ruger+security+9&sxsrf=ACYBGNS_NnswNBmt32am4Zb2vq1fcREieQ:1577047076923&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiR7MCWjsrmAhUim-AKHU92Cv0Q_AUoAnoECAwQBA&biw=1280&bih=596#imgrc=9Eo9jN0NwKLVaM:

yes it will fit the ruger security 9 just fine The Streamlight TLR-4 is a lightweight weapon-mounted tactical light with an integrated aiming laser. This weapon mount light has a powerful C4 LED with 110 lumens. The Streamlight TLR-4 provides 1.5 hours of continuous runtime when using both the C4 white LED and red laser. The rail clamp on the Streamlight TLR-4 is designed for rapid attachment/detachment and fits a wide range of weapons with the included key kit.
Specifications and Features:
Powerful C4 LED technology, 110 lumens
Red aiming laser, 640-660nm (Class 3R laser, max output less than 5 mW)
Runs for 1.5 hours in dual mode - using C4 white LED and red laser
Runs for 11 hour when using laser only
Ambidextrous three position switch
Momentary on or constant on/off
Choose laser only, C4 white LED only or both laser and white LED
One handed snap-on and tighten for attaching to and detaching from weapon
Optimized electronics provides power regulated brightness
Textured parabolic reflector produces a concentrated white center beam plus optimal peripheral lighting
Fits subcompact, compact and full-size handguns with rails
Constructed of impact resistant and lightweight engineering polymer
Borofloat high temperature glass lens
Dust proof and shock proof
IPX4 rated - water resistant operation
Measures 2.73"L x 1.2"W x 1.99"H
Weighs 2.81 oz with batteries
Includes battery and key kit to securely fit a broad range of weapons
assembled in USA
Limited lifetime warranty through Str