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What size screws should be used? Also, what length of tubing is required to provide the height for Z-Axis height, for instance the default of 4" of usable work height? The corner leg conduit lengths would be 4" - 0.5" = 3.5". I am struggling with my 3D printer and wanted to pick up or order the screws before printing. Plus the measuring tool in NetFabb is not working for me . These span supports are going to be great though, once I get them printed :). Thank you!