How to tighten security screw with H pattern on bike seat?

Question

My bike seat has a bolt connecting it to the seatpost, which has come loose. The bolt on the underside of the seat is standard and can be turned with a hex wrench, but it's connected to what I believe is a security screw (pictured below) which needs to be held in place or turned in the opposite direction: otherwise the bolt and the security screw spin freely together. The security screw isn't the typical security torx: it has a very shallow H shaped indent in it instead. It's shallow enough that I wonder if it could even hold the screw in place while the bolt turns, but I don't see anything else to grip onto since the security screw is perfectly round. Searching for bike H screws returns derailleur H limit screws, so it's been hard to find anything on this.

Is this a standard type of security screw I can buy a tool for? The seat is from Selle Royal, and the seatpost is from an Azor (Amsterdam-based company) bike.

Answer 1

You are looking at the end of the bolt. If you look under the post there should be access to a regular hex head.

The "H" may be an indicator (Hardened ?) for the grade of the bolt or a manufacturer mark.

The torque rating for a seat post bolt generally will be in the order of 10-15 Nm. I.e quite a lot but not too much if using a wrist-o-meter.