Thumb Screw on a Cherry MX backlit key cap. R4, 1x1 size. 

International Customers: Our apologies for the excessive shipping price of these key caps. Starting January 2019 US Postal Service has changed their International First Class Mail policies and no longer accept "thick envelopes". Key caps now need to be shipped as a package which increases the shipping price by 250%. Our apologies for this idiotic shipping charge.