The easiest thing to do is measure the height of the lower framework on the lift. The extrusions that connects each upright should measure roughly 2” wide x 4” tall for a 2600 or 3000 lb capacity and should measure roughly 2” wide x 5” for a 3600 or 4000 lb capacity. This will determine the weight capacity and the first portion of the model number. Then measure the inside width from upright to upright across the lift. This will either measure 108” or 120” and this will give you the max beam or the section part of the model number. So if the lower framework measures 2” x 4” and the inside width is 108”, then you either have a 26108 or a 30108. If the lower framework measures 2” x 5” and the inside width is 120”, then you either have a 36120 or a 40120. If you have a flat rack I-beam aluminum cradle cross member, add SS to the front of the number. If you have a V-rack galvanized steel cradle cross member, then add an SSV before the number. Examples being SS26108 or SSV36120. This model number is crucial when discussing replacement or repair parts for your lift with any dealers or distributors. Without this information it can be very difficult for anyone to accurately recommend a course of action. The last thing you want is to order parts and have them shipped out only to discover right before the summer season that you have got the wrong size parts and now have to pay shipping for them to be returned and then reorder the correct ones.