diff --git a/scad/bolex_base_plate.scad b/scad/bolex_base_plate.scad
index 70a53d9..6ee6049 100644
--- a/scad/bolex_base_plate.scad
+++ b/scad/bolex_base_plate.scad
@@ -3,6 +3,8 @@ use <./common/common.scad>
 PLATE_X = -6;
 PLATE_Y = 25;
 
+RAIL_SPACING_HALF_IN = 30;
+HALF_IN_RAIL_D = 13;
 
 module bolex_debug (pad = 0) {
     cylinder(r = R(29) + pad, h = 10, center = true, $fn = 80);
@@ -94,8 +96,8 @@ module base_plate (pos = [0, 0, 0], rot = [0, 0, 0], rails = "15mm") {
                     }
                 }
             } else if (rails == "1/2in") {
-                translate([15, -50, 0]) rotate([90, 0, 0]) cylinder(r = R(13), h = 100, center = true, $fn = 50);
-                translate([-15, -50, 0]) rotate([90, 0, 0]) cylinder(r = R(13), h = 100, center = true, $fn = 50);
+                translate([RAIL_SPACING_HALF_IN / 2, -50, 0]) rotate([90, 0, 0]) cylinder(r = R(HALF_IN_RAIL_D), h = 100, center = true, $fn = 50);
+                translate([-RAIL_SPACING_HALF_IN / 2, -50, 0]) rotate([90, 0, 0]) cylinder(r = R(HALF_IN_RAIL_D), h = 100, center = true, $fn = 50);
             }
             
         }