Prop Nuts
Saito prop nuts

Above: Washer, prop nut and smaller lock nut for Saito 120,150,180.  This is part number ‘170R3-28’.    Note: the washer is flat on the surface where the flat surface of the nut comes in contact.

Saito nut packets

Washer and nuts for Saito 120,150,180: On the left side of this page shows the lock-nut prop washer system. Above are shown a different type of washer and nut. On the left in the above picture is the washer and nut that came with all older engines. The washer has a concave center part that matches the convex portion of the mating nut. The Saito part numbers are 120-28A  or  SAI270T28A  The bag on the right in the picture above contains a similar nut but is longer and is called ‘Prop Nut for Spinner’ on the package and is Saito part number 120-29 or 120S-29; the Horion Hobby part number is SAI120S29. These spinner prop nuts have a 5mm tapped thread and are ideal for Tru-Turn spinners. Horizon Hobby sells the matching prop washer alone; it is Saito part number 130T-137 and Horizon Hobby part number SAI130T137.

USING A SPINNER: Plastic spinners are unsuitable for engines like the Saito-91 and larger; plastic spinners can be used with care on the larger engines, however a backfire may break the spinner. TruTurn spinners work well for these bigger engine sizes and these are attached via a 5mm bolt through the front of the spinner. The adapter nut may be purchased from Tru-Turn for all Saito engines. Alternatively, for the 100, 120, 150, 180 you can use the above Saito ‘prop nut for spinner’ (part 120S-29) and matching prop washer (part 130T-137) and you will not need the Tru-Turn adapter; however there is no lock nut with this option, and you are likely to lose the nut and spinner if the engine backfires in the air.

Thread size for the Saito-30 and Saito-40 is 1/4-28 --- all other Saito engines use metric thread sizes. The thread size for the 50,56,65,72,80,82,91 engines is 7x1mm.The thread size for the 100, 120,150,180 engines is 8x1.25 mm

Tru-Turn Spinner Adapters:   Tru-Turn make nuts and spinner adapters that are suitable for Saito engines. When using the Tru-Turn adapter a single Saito prop nut may possibly be used first, then a Tru-Turn adapter nut may be added which acts as a jam nut, and as a receptacle for a 5mm (or 10-32) bolt to hold the spinner. However this usually won’t work for most props that are too thick. For engines with thick props there may be too little thread for both a Saito nut/washer plus an adapter nut to hold a spinner. 

65, 72, 80, 82, 91  Engines:  These engines use a 7x1 mm thread. Use Tru-Turn Adapter Kit  TT-0718-A  (7x1.0mm/8mm); this adapter does not have a jam nut. Another adapter TT-0717A has a jam nut and is the one recommended on the Tru-Turn web site.

100, 120, 125, 150, 180, 220 engines:   These engines use a 8x1.25 mm thread. The 180, and new updated 150 engines (possibly also 120’s ???) now have slightly longer propshafts. The older short lengths are about 3.8 cm from prop hub to tip of the propshaft, whereas the newer engines are 4.2 cm length. Depending on the thickness of your prop, and the particular propshaft length, you may need either of two Tru-Turn adapters (a) the TT-0822-A  (probably better for shorter shafts), or (b) TT-0823-A (maybe better for longer shafts on 150 and 180 engines); these adapters include washer and lock-nuts and you won’t need the Saito nut and washer that came with the engine. Overall, getting a spinner to fit with the right adapter and right length bolt can be a real pain. Chances are that the TT-0823-A adapter will work for you; if you have a very thick prop you may have to try the TT-0822-A version. The adapter TT-0825A will also work but does not have a jam nut.

The bolt (5mm thread) that comes with Tru-Turn spinners maybe the wrong length for your particular setup and getting a suitable size replacement can be a challenge.

Another way to hold the spinner on the 120/150/180 engines is to use the Saito washer and nut part number 120S-29. This is a large nut that includes a 5mm threaded hole for the prop bolt to attach. This works well with Tru-Turn spinners but there is no lock nut.


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Saito-150 with old-style muffler