The Atwood Springlift SL31-40-1 is a low-cost gas spring. See below for more information. The SL31-40-1 is like the SL31-30-1 except its standard output force is 40 Ibs instead of 30 Ibs. The SL31-40-1 gas spring is 7.5 long when expanded and 5.25 long when closed. Ball socket type ends are 10mm with a stroke of 2.25 and a standard output force of 40 Ibs. Marines best low-cost gas spring; when cosmetics and stainless rust resistance are not a concern this is your best option