Comparison of action slide lengths: top 7-5/8”, bottom 6-1/2” Measure from top of threads to bottom of collar that holds the action bars. This measurement is critical to fit when ordering forearms or stock sets that include a forearm. For the most part, 20-year and older sporting shotguns and new tactical shotguns use the 7-5/8” slide. New sporting models have used the 6-1/2” slide for almost 20 years. There are exceptions, however. To be sure, measure! NOTE: Since 2006, most new 500,535, 835,Ulti-mag and Maverick 88 sporting shotguns with synthetic forearms may not use an action slide tube at all; rather, the pump handle will have two integral bars pinned into the handle itself. If you have one of these, you cannot use a forearm that was designed to go over an action slide tube without first buying the correct length tube and action slide tube nut. You may contact Havlin Sales at 636/937-6401 to obtain proper components.