Chris, aka nop.head - your tip about viewing in Orthogonal instead of Perspective is worthy of a Big Thank You - a festive tipple of your choice, pint of Robinson's perhaps? If I am differencing cylinders to make a tube, I use a default offset of 0.1, but assigned to a 'constant', which I called cd, then I make the length of the inner cylinder plus 2xcd.  It makes offsetting so much easier when I use a module that makes the hole and puts a chamfer either side of the hole thus: module chamfered_hole_45 (hole_dia,plate_thick,hole_cham=1,bolt_round=40) {   echo (hole_dia,plate_thick,hole_cham,bolt_round);     //bolt_round = 40;     hole_depth = 2*plate_thick ;// just makes a long pole :-)     l_hole_dia = hole_dia;     l_hole_cham = hole_cham;     echo (hole_depth=hole_depth);     echo (bolt_round=bolt_round); cylinder(d1=l_hole_dia+l_hole_cham*2,d2=l_hole_dia,h=l_hole_cham,$fn=bolt_round);     cylinder_outer (l_hole_dia/2,hole_depth+1,bolt_round);     translate([0,0,plate_thick-l_hole_cham]) cylinder(d1=l_hole_dia,d2=l_hole_dia+l_hole_cham*2,h=l_hole_cham,$fn=bolt_round); }//end module cylinder_outer is another module that compensates for the geometry going round the inside of the 'hole' and making it undersize. module cylinder_outer(radius,height,fn){    fudge = 1/cos(180/fn);    cylinder(h=height,r=radius*fudge,$fn=fn);} Compliments of the season to all our readers ;-) Roger