Ok- ABS is a type of plastic. It has nothing to do with size, but all I've seen are schedule 40 and black. Schedule 80 bulkheads I've used are grey and not ABS. Usually look much heavier duty. A 1 inch 40 pipe is a very loose fit in a 1 inch 80 slip bulkhead and won't work (except in cases where a little leaking in not a problem, e.g. an internal over flow).
Scheduled 80 bulkhead holes are bigger than 40, but vary a little between brands. Nothing a rasp or Dremmel wont fix.
Sounds like you are attempting to attach an un -threaded flex hose from your overflow to your sump? That presents a whole different set of issues, all of which are easily solvable, if we had the big picture of what you seek to accomplish.