Our extender screw is the same on all our models, so you don't have to worry which one to order based on model. It is a M8 high tensile cap screw specifically designed to connect an extender to the main seat frame. You can also use any M8 high tensile screw from your local hardware store; as long as it is M8 high tensile around 20mm long, it will work even if it's not exactly the same style screw head!
Let us know if you have any questions!
It is also the same screw that connects the extender to the t-bar at the other end.