TrigpointingUK

I'm new to trigpointing and until very recently I thought of a trig point as the type of pillar you often find at the top of a hill. I'm very quickly realising they come in different forms and that there is a lot that can be learnt about them. Right now I have a few questions about intersected stations and I am hoping you can help me.
As a result of using your website I realised that the weather vane at the top of Penistone Church tower is an example of an intersected section but what is an intersected station? I have seen that some people have logged photographs of the weather vane and what I assume is the installed mark on the wall beside the church door but they have logged the visit as not inspected. Is that because the actual trig point is the weather vane and/or the installed mark that should be near or on the vain is the trig point?
What is an installed mark?
The mark on the outside of the church wall had a bolt/screw. What is that?
Thank you an anticipation of any help.

Hi, you might find the T:UK wiki pages quite helpful.

Basically an intersected station is an observable point to which the OS took readings; there is no physical mark present.

The mark near the door is not a triangulation station, but a benchmark. The two are not directly connected in any way, except in the sense that church buildings tended to be thought of as permanent features of the built environment, and therefore very suitable for OS purposes.

Hi & thanks for this.