String Trimmer & Blower Bolt & Torque Specs

OEM-referenced torque specs and fastener sizes for string trimmers and handheld 2-stroke blowers: Echo SRM-225/GT-225 and the Echo PB-8010T backpack blower, plus comparable Ryobi and Stihl 2-stroke trimmers. Covers trimmer head bolts, clutch housing bolts, and spark plugs.

Trimmer head and cutter fastener — reverse thread, and Echo does publish a figure

The head or blade adapter threads onto the drive shaft with a left-hand (reverse) thread so rotation cannot loosen it: turn clockwise to remove. A plastic string head is genuinely a hand-tight-plus-a-quarter-turn part with no published torque. The metal cutter fastener is not — Echo’s SRM-2620ES service manual specifies its LM10 left-hand cutter fastener at 28-32 N·m (about 21-24 ft-lb), the highest torque on the machine. If you are fitting a blade rather than a string head, look the figure up for your model instead of assuming none exists.

Spark plug and clutch torque, as Echo prints them

Echo’s SRM-225 manual specifies 130-150 lbf-in for the spark plug — about 10.8-12.5 ft-lb, or 14.7-16.7 N·m — and the identical lbf-in figure appears in the CS-400 and CS-590 chainsaw manuals, so Echo uses one plug spec across the range. The SRM-2620ES service table gives 10-15 N·m (about 7-11 ft-lb) for its M10 plug, lower again because the thread is smaller. For the clutch, that same table specifies 7-11 N·m (62-97 in-lb) on the M6 clutch shoe. All of these are bands rather than single targets, and all of them are well under what a chainsaw M14 plug takes — match the figure to your machine, not to "2-stroke".

Carburetor, muffler and spark-arrestor screen

These are the fasteners where a guess costs a part, and the published figures are further apart than they look. Stihl specifies 2.7 N·m (24 in-lb) for the MS 210/230/250 filter housing and carburetor. Echo’s SRM-2620ES gives 7-11 N·m (62-97 in-lb) for the muffler itself but only 2.5-3.5 N·m for the starter-side muffler cover screw and 3-4.5 N·m for the crankcase-side one — Echo really does give the two sides of the same cover different numbers. The spark-arrestor screen is lower still: Stihl specifies 1.0 N·m (9 in-lb) on the MS 261, which is screwdriver feel, not wrench feel. Where a manufacturer publishes nothing for a small fastener, Echo’s general table is a defensible fallback: M4 1.5-2.5 N·m, M5 2.5-4.5, M6 4.5-7.5. Clean or replace the arrestor screen at every muffler service.

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