+catch_pin_width = rivet_entry_width - catch_pin_gap;
+
+cppy6 = -catch_strap_width/2;
+cppxC = TAU * 0.34 * main_dia/2;
+cppB = [ catch_pin_width/2,
+ cppy6
+ + catch_stem_below_gap
+ + catch_pin_height
+ + catch_knob_dia/2 ];
+cpp0 = [ 0,
+ cppB[1]
+ + catch_knob_dia
+ + catch_knob_above_gap ];
+cpp12 = cpp0 + [1,0] * (catch_pin_height * catch_hook_slope);