diff --git a/src/frames/pieces/box/side-inner-wall.scad b/src/frames/pieces/box/side-inner-wall.scad
new file mode 100644
index 0000000..9fd4b73
--- /dev/null
+++ b/src/frames/pieces/box/side-inner-wall.scad
@@ -0,0 +1,24 @@
+/* The inner side wall of the frame, for being displayed through a windowed part.
+ *
+ * SPDX-FileCopyrightText: © 2024 Brian S. Stephan <bss@incorporeal.org>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+include <parameters.scad>
+include <components.scad>
+use <frame-piece-side-for-box.scad>
+
+module side_inner_wall_frame_piece() {
+	difference() {
+		side_box_frame_piece();
+		// minus the outer wall
+		translate([-(frame_x-frame_wall)/2, 0, 0]) cube([frame_wall, frame_y, frame_z], center=true);
+		// minus half of the mounting posts (the other half provided by the outer wall)
+		translate([-panel_to_frame_point_x, panel_to_frame_point_y, frame_z/2]) rotate([0, 0, 90])
+			frame_mount_column();
+		translate([-panel_to_frame_point_x, -(panel_to_frame_point_y), -frame_z/2]) rotate([0, 0, 180])
+			frame_mount_column();
+	}
+}
+
+side_inner_wall_frame_piece();
diff --git a/src/frames/pieces/box/top-or-bottom-inner-wall.scad b/src/frames/pieces/box/top-or-bottom-inner-wall.scad
new file mode 100644
index 0000000..5ba4c63
--- /dev/null
+++ b/src/frames/pieces/box/top-or-bottom-inner-wall.scad
@@ -0,0 +1,24 @@
+/* The inner top/bottom wall of the frame, for being displayed through a windowed part.
+ *
+ * SPDX-FileCopyrightText: © 2024 Brian S. Stephan <bss@incorporeal.org>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+include <parameters.scad>
+include <components.scad>
+use <frame-piece-top-or-bottom-for-box.scad>
+
+module top_or_bottom_inner_wall_frame_piece() {
+	difference() {
+		top_or_bottom_box_frame_piece();
+		// minus the outer wall
+		translate([0, -(frame_y-frame_wall)/2, 0]) cube([frame_x, frame_wall, frame_z], center=true);
+		// minus half of the mounting posts (the other half provided by the outer wall)
+		translate([-panel_to_frame_point_x, -(panel_to_frame_point_y), frame_z/2]) rotate([0, 0, 180])
+			frame_mount_column();
+		translate([panel_to_frame_point_x, -(panel_to_frame_point_y), -frame_z/2]) rotate([0, 0, 270])
+			frame_mount_column();
+	}
+}
+
+top_or_bottom_inner_wall_frame_piece();
diff --git a/src/frames/pieces/box/top-or-bottom-windowed.scad b/src/frames/pieces/box/top-or-bottom-windowed.scad
new file mode 100644
index 0000000..6327e28
--- /dev/null
+++ b/src/frames/pieces/box/top-or-bottom-windowed.scad
@@ -0,0 +1,23 @@
+/*
+ * SPDX-FileCopyrightText: © 2024 Brian S. Stephan <bss@incorporeal.org>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+include <parameters.scad>
+include <components.scad>
+use <frame-piece-top-or-bottom-for-box.scad>
+use <top-or-bottom-inner-wall.scad>
+
+module windowed_top_or_bottom_box_frame_piece() {
+	difference() {
+		top_or_bottom_box_frame_piece();
+		// subtract frame wall window
+		translate([0, -frame_y/2, 0])
+			cube([frame_x-frame_mount_column_width*3.5, (frame_wall+panel_support_width)*2,
+				frame_z-panel_z*3], center=true);
+		// subtract the inner wall area that will be provided by the other piece
+		top_or_bottom_inner_wall_frame_piece();
+	}
+}
+
+windowed_top_or_bottom_box_frame_piece();