When I got this I was confused. There are many different seals, but there is only one dosing diaphragm. I think multiple spacers are meant to support multiple different carburetors. There were no instructions for this at all, so it was a bit difficult for me to get the right seal/diaphragm. Thank god for YouTube for installing the seal and metering diaphragm in the wrong order (that's how they were installed when I got the used trimmer). But now everything works great!