If you are not sure which type of perforations you need for your film leader, the Australian Film Archives have a great resource on BH vs KS film perforations, including also a variety of different widths of film:
https://www.nfsa.gov.au/preservation/preservation-glossary/perforationsOr for information on specifically film leaders, there's a page on wikipedia all about film leaders:
https://en.wikipedia.org/wiki/Film_leader