Not quite what I've done but what I've tried to do. Went to change my vac pipe that has the pill in. Ordered 3mm and 5mm to do most of the pipework. What size is the restrictor pill? It won't fit in 3mm and slips out of 5mm. Before I go order 4mm I wondered if I have been given the wrong size. I can jam it in the "3mm" but I don't think it should be that snug.