How to Choose the Right Flywheel Puller Thread Size

Choosing the right flywheel puller comes down to three measurements: thread diameter, thread pitch, and thread direction. This guide explains how to identify each one and avoid the most common mistake - stripping the flywheel threads with the wrong puller.

The Three Measurements That Matter

1. Thread Diameter (the "M" number)

The M number is the outer diameter of the thread in millimeters. M27 means a 27 mm thread, M28 means 28 mm. This is the most obvious measurement, but the pitch is what trips people up.

2. Thread Pitch (the "×1.0" part)

Pitch is the distance between adjacent threads. A M27×1.0 and a M27×1.25 are DIFFERENT pullers - they look nearly identical but the finer pitch will not thread onto the coarser one. Common pitches are 1.0 mm, 1.25 mm and 1.5 mm.

3. Thread Direction (RH vs LH)

Most flywheels use a right-hand (RH) thread, but some - especially GY6 scooters and certain MX/dirt bike engines - use a left-hand (LH) thread. Using an RH puller on an LH flywheel will not engage properly.

4. Internal vs External Thread

Some pullers thread INTO the flywheel (internal/female), others thread OVER the flywheel (external/male). Check whether your flywheel has a threaded hole or a threaded boss.

Common Sizes and What They Fit

• M27×1.0 LH - the most common size for GY6 125/150 scooters and many Japanese MX/dirt bikes.
• M28×1.0 RH - Honda CRF150R/250R/450R, Kawasaki KX250F/450F, Suzuki RM-Z250/450, Yamaha YZ450F.
• M26×1.0 RH - KTM 250/400/450/520/525 RFS engines.
• M38×1.5 RH - Suzuki DR-Z400, LT-Z400, Kawasaki Ninja 650, Versys 650.
• M33×1.5 RH - KTM 620-690 LC4, Suzuki GSX-R600/750/1000, Yamaha WR450F.

How to Measure Without a Manual

1. Clean the flywheel center so the threads are visible.
2. Use a caliper to measure the thread outer diameter.
3. Use a thread pitch gauge to find the pitch (1.0 / 1.25 / 1.5).
4. Look at the thread angle - RH threads slope up to the right, LH to the left.

What to Do If You Are Not Sure

Do not guess - a wrong puller can destroy the flywheel. Send NACHEE your motorcycle make, model and year, and we will confirm the correct puller size for free. Our catalog covers M14 to M50, so we almost certainly have the size you need.

Website: https://www.nachee.cn
Email: lilywang@nachee.cn
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