$fn = 64;

// --- Parameters ---
rail_length = 800;       // Total length of the rail
rail_width = 30;         // Total width of the rail
rail_height = 15;        // Total height/thickness of the rail

slot_top_width = 8.5;    // Width of the top opening (fits M8 bolt shaft or M4 screw head)
slot_top_depth = 6;      // Depth of the top opening
slot_base_width = 18;    // Width of the inside slot (fits standard M8 bolt head/nut)
slot_base_depth = 5;     // Depth of the inside slot

hole_spacing = 100;      // Distance between mounting holes
hole_diameter = 4.5;     // Mounting hole size (M4 clearance)

module t_slot_rail() {
    difference() {
        // Main solid body
        cube([rail_length, rail_width, rail_height]);
        
        // Top narrow slot
        translate([-1, (rail_width - slot_top_width) / 2, rail_height - slot_top_depth + 0.1])
            cube([rail_length + 2, slot_top_width, slot_top_depth]);
            
        // Bottom wide slot (T-section)
        translate([-1, (rail_width - slot_base_width) / 2, rail_height - slot_top_depth - slot_base_depth + 0.1])
            cube([rail_length + 2, slot_base_width, slot_base_depth]);
            
        // Wall mounting holes (centered in the slot)
        for (x = [hole_spacing/2 : hole_spacing : rail_length]) {
            translate([x, rail_width / 2, -1])
                cylinder(h = rail_height + 2, d = hole_diameter);
        }
    }
}

// Center the model for easier viewing in the slicer
translate([-rail_length/2, -rail_width/2, 0])
    t_slot_rail();