Many of the gun manufacturers have different choke systems and ways of identifying which system is on your gun. These can usually be found on the manufacturers website. If you can't determine which choke it is from this, then please view the product images on our website. All of the products on our website have a measurement next to the choke to show the length of the choke. Please compare these images to an existing choke in the gun. Take particular note of the overall length of the internal section of the choke, the thread position and the thread length. If you are still unsure of which choke to order, please send an image of an existing choke next to a ruler or tape measure to firstname.lastname@example.org and we will happily advise if it is a choke model we currently make.