YES 40 FS/FI Storefront System The Screw Spline Assembly method uses a two piece vertical mullion. This allows the frame to be constructed in units using screws driven through the back of the vertical mullions into the screw splines of the horizontal members. The units are then snapped together at the vertical to complete the fabrication. Effective Date: Aug 23, 2024 | 02-1001-04 Page-3