Sash Window Query

[Newhome]

Hi guys,

Hopefully a very quick query but I need some clarification regarding sash windows and their opening mechanisms.

I am replacing a single glazed bay window with a double glazed unit and the firm I have found has given me two options in the way the windows slide (as apparently the the tradional weight/pulley option is not possible).

The first is the Sprial Balanced option - which after a bit of research I'm now aware of but the second option (and the area I'm struggling on) is a Friction Hold mechanism.

I can;t seem to find any information on this on the internet and was hoping someone would be able to give me some more details on this.

Thank in advance