-// attachment point move up so clears when inserted
-// onejig must be deep enough for strap plus motion plus holder
-// even deeper for side rails
-// what about existing slot locator ? maybe not
+// various registration marks
+// protrustions at ends at strap width and middle
+// grooves on top face at 1/4,1/2,3/4 length and 1/2 width