When you enter the make, model and year of your car in the search box and click on the search icon, the boss kit for your car will automatically be selected. On the top of every page there are links to 'Steering Wheels', 'Bosses' and 'Accessories'. Click each one in turn and the recommendations for your car will be shown.
Please see guide to accessories for the photo of the different sizes or the billet horn buttons or caps (3.5" (shows fixing screws) or 4.5" (covers fixing screws)