ap_width = 21.30;
ap_height = 16.45;
-tot_height = 22.74;
+tot_height = 22.74 + 1.0;
screw_ctr_to_tr = [ 7.89, 3.87 ];
tab_th = 2.5;
wall_th = 1;
-wall_h = 1;
+wall_h = 2;
app_slop = 0.60; // total across both sides
tab_h = tot_height - ap_height;
-real_ap_sz = [ ap_width, ap_height ] - app_slop * [ 1,1 ];
-real_main_sz = real_ap_sz + wall_th * [ 2,1 ];
+real_main_sz = [ ap_width, ap_height ] - app_slop * [ 1,1 ];
real_all_sz = real_main_sz + tab_h * [0,1];
+real_inner_sz = real_main_sz - wall_th * [ 2,1 ];
screw_pos = real_all_sz - (screw_ctr_to_tr - 0.5 * app_slop * [1,1]);