A lot of aluminium jobs need both a finish on the end of the post and an opening along the rail, frame or batten.
Those are different jobs.
The end of the extrusion is an end cap. Nelsons CNC machines a knock-in aluminium cap to the size of the post or tube, so it taps in with a mallet. No weld, no glue. That's what this site is for: aluminium end caps, including custom sizes when the extrusion isn't a standard size.
A slot, louvre, lock box or wheel cut-out isn't an end cap. That's material taken out of the length so a screen, gate or rail can assemble. That work is done by Nelsons Routing. Nelsons Routing is a separate business. It shares our Sunshine Coast factory. It doesn't sell the end caps, and Nelsons CNC doesn't run the routing job.
Send the cap with the extrusion size. Send the cut-out with a drawing (.DXF or .DWG) and the spacing you need. If you aren't sure which one you need, look at where the work sits: on the open end, it's a cap. Along the length, it's routing.