it's a very simple one piece mold. you simply pour in the hot plastic, let it cool for ten seconds or so (depending on plastic temp, mold temp) then turn the mold upside down, drain the still hot, fluid plastic out of the mold for ten seconds or so, then reright the mold to cool. the outside of tubes comes out perfect every time. timing is everything as far as tube wall thickness goes. i've had some tubes come out half solid, with thick walls, but after a little experimenting, i've got it down. pros; you only have heat enough plastic to fill the cavities and the tubes exterior always comes out perfect.