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(3PACK) Speed-Feed 450 Fast Loading Bump Trimmer HEADS for ECHO SRM Trimmers PART# 99944200903This model holds approximately 20' of .095" diameter trimmer line, and accepts line sizes up to .130"
it comes pre-loaded with .095" CrossFire line, with the included instructions and adapters
This item fits ECHO SRM models with an engine displacement over 25cc's.  For example, BUT NOT LIMITED TO, SRM-266, SRM-266S, SRM-266T, SRM-280, SRM-280S, SRM-280T, SRM-266U, SRM-280U, SRM-410U, PAS-280.
If you have under 25cc's, it is recommended that you purchase the Speed Feed 400.  These machines include SRM-210, SRM-225, SRM-230, etc.  You can find the information on your engine displacement in your owner's manual.

This head is extremely heavy for the smaller machines!
If you are not sure, just ask!  We are here to help you with your purchase!