Mastic / Alcoa EZ Corners fit a 5/8"WM j-channel and are available in only white. The Alcoa brand EZ Corners have a matt finish. E-Z Corners work around windows, porch ceilings, and soffit; wherever J-channel is used as a receiver or as trim. The E-Z Corner is nailed in place and the J-channel simply slips into it. These E-Z Corners are designed to be used with 5/8 inch Mastic or Alcoa j-channel.