Nockturnal lighted nocks are a breakthrough design that combines ultra-light performance with a high visibility light source and "instant on" simplicity that activates upon release. 

The patent-pending string-activated "hidden linear switch" is protected deep within the nock and will not turn on or off inadvertently.  Battery life is over 20 hours. 

-Nockturnal S fits most "standard sized" carbon hunting arrows such as:

Beman ICS

Easton 

Carbon Express

PSE

Carbon Tech

Victory

Carbon Impact

And most other arrows icluding aluminum arrow with a super-UNI bushing