I replaced the gas spring on my Dunco (max paper size 30x40) a few years back. The new spring has a coding written on it: W06 ZBP 0050. This makes me think it is a 50 Newton spring. That is working OK but I would recommend something stronger. This spring does fine when the frame is all the way up but when printing smaller formats the enlarger head may get in the way and you cannot open the frame all the way up. My spring is not strong enough then, the frame falls down. So if this is indeed a 50 Newton spring I would recommend something like 70 to 100 Newton.