I recently picked up a two-tone Heuer 1000 980.021N without a case-back. I have a two-tone 1000 980.020N and the case-back from it fits the 980.021N; both watches run properly. The larger watch needs a case-back, and the threads are 29.75mm. Any man’s Heuer 1000 case-back should fit, so I’d be interested in any genuine Heuer case-back that will fit. Please let me know what you might have. Thank you.