This is a pretty common issue as there’s a seemingly endless range of collets/spacers/bolts for these things.
Back in my tree days the landscape boys had a big box of bits for exactly this reason.
When you bought the strimmer did it come with any additional parts? My cheapo strimmer had a couple of collets for the various heads.
Sometimes it’s a bit like angle grinders where you just need to remove/flip over the spacer/locknut for various things.
Sorry I can’t help better but in my experience getting various strimmer attachments to work in harmony has always been a ballache…
This is a pretty common issue as there’s a seemingly endless range of collets/spacers/bolts for these things.
Back in my tree days the landscape boys had a big box of bits for exactly this reason.
When you bought the strimmer did it come with any additional parts? My cheapo strimmer had a couple of collets for the various heads.
Sometimes it’s a bit like angle grinders where you just need to remove/flip over the spacer/locknut for various things.
Sorry I can’t help better but in my experience getting various strimmer attachments to work in harmony has always been a ballache…