I don’t have pics but I made the limiter from brass tubing. I soldered a larger tube over the smaller tube as a shoulder feature to keep the main tube from going inside the end cap and smashing the o-ring. Make the smaller dia. tube the length you require and then add an 1/8 inch long sleeve/shoulder to be the stop. I used some digital calipers to measure the length and make them equal. Used a tube cutter and file to get them to length.
The cap on the Robart air cylinder just unscrews easily, no thread lock that I have seen on any I’ve taken apart.
By the way, take apart these cylinders and clean out the white grease. I replaced it with thick silicone RC oil and used just a couple drops. These don’t stick and move with very little air pressure now.
I’ll see if I can snap a quick pic for you...