Does anyone know

[kingmt]

What is this slotted cap, nob, or something else is in the corner of the turrets by the parallax control.

 

[macgrumpy]

What brand/model scope?

 

[kingmt]

Sorry I meant to include that in the first post. Is a Chinese scope branded NOS 10-40x50.

 

[Howard Roark]

It's probably how the scope manufacturer installed the erector tube return spring. It could also be a locking mechanism to lock the spring in place to eliminate movement, like a Burris Posi-Lock. Although, they typically have an external adjustment knob, not a slot head screw. My guess would be the former rather than the later.

Below is a good write up on how a scope works with illustrations.
http://precisionrifleblog.com/wp-content/uploads/2014/08/how-a-rifle-scope-works1.png

 

[Arizona_Mike]

Could be a the bleed screw for the nitrogen pure, in which case you don't want to loosen it.

 

[Bart B.]

Is it mentioned in its user manual?

Pictures too dark to see the details.

 

[kingmt]

No

It's Chinese glass so there isn't very much information.

 

[imashooter]

It's probably how the scope manufacturer installed the erector tube return spring. It could also be a locking mechanism to lock the spring in place to eliminate movement, like a Burris Posi-Lock. Although, they typically have an external adjustment knob, not a slot head screw. My guess would be the former rather than the later.

Below is a good write up on how a scope works with illustrations.
http://precisionrifleblog.com/wp-content/uploads/2014/08/how-a-rifle-scope-works1.png

Good call. Paragraph 7 in this link (different scope) gives a brief description: http://www.japanoptics.co.jp/html/pdf/jol_manu.pdf