Kiln-dried SPF lumber runs through precision CNC mills to create these tongue-and-groove strips, ensuring joints lock together without gaps or wobble. That 1-3/8 inch square profile provides the structural depth galleries expect while the gradually tapered lip keeps stretched canvas from touching the frame's back edge, crucial for preventing impressions that telegraph through your painting surface.

The tongue-and-groove system eliminates the frustration of misaligned corners that plague simple butt-joined frames. Each strip interlocks with its neighbor, creating stable right angles that stay square under canvas tension. This precision matters when you're stretching large formats or working with heavyweight canvas that exerts serious pull across the frame.

Fredrix sells these individually rather than in pre-cut sets, letting you build custom dimensions without waste. Need a 37 x 51 inch format? Buy exactly what you need. The consistent milling tolerances mean strips from different orders still fit together seamlessly, useful when expanding a series or replacing damaged pieces. Gallery-depth frames project confidence on exhibition walls while providing clearance that protects your painted surface from contact damage during handling and transport.