I haven't converted an Echo weed*wacker or hedge trimmer, but I have converted an Echo chainsaw (30 cc). *Echo makes a really good engine. *I'm not sure of the thread size on the Echo, most hubs I've machined for the engines I converted are 5/16-24. *The threads on an Echo may be metric (not sure as I never converted one) *The hub I made for the chainsaw bolts to the flywheel (like a Zenoah), instead of screwing on the crankshaft.
Jeff Pittel