Even here in the UK BA taps and Dies are starting to go up in price because the metric system has now taken over in a big way suppliers claiming that the turnover BA has dropped considerably. Though it is ironic that BA stems from a metric platform, and I have also found some shotgun front sight threading to be British ME (model engineering) thread form. Though it will be a good chance that BA will be the correct threading but with Brit guns you can never be certain.

The only lessons in my life I truly did learn from where the ones I paid for!