OS .15 (2.5cc) Max I, Max II and Max III

[Steve Helmick]

Does anybody have any of the above and know how to measure the prop shaft thread? I am not sure they'd all be the same. I only know that the .15FP and .15LA are 7/32-32, and there's reason to believe the earlier ones were NOT 7/32-32.

Some Free Flight friends need to know, and I may be involved in helping them adapting 1.25" spinners (likely Brodak's 1/2A item) to their engines. I can measure the pitch and major diameter, but I don't have any these .15's, and the nearest one I know of is near Oregon City.  Steve

[Steve Berry]

Here's what I've found.

https://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/11365200-os-15-iii-rc-prop-nut-5-5x-8-a.html


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[John Lindberg]

This fellow made me a spinner nut so I could use an electric starter for my OS Max II-http://www.flyfreeflight.com/Site/Home.html

[Tim Wescott]

You're a machinist, Steve -- you could turn the thread without needing a tap 

[Tim Wescott]

I don't have any itty bitty precision wires lying around, and I know measuring the OD is not precise -- but the OD of the threaded portion of three of my OS III 15's measures 0.215".

[Dallas Hanna]

Does anybody have any of the above and know how to measure the prop shaft thread? I am not sure they'd all be the same. I only know that the .15FP and .15LA are 7/32-32, and there's reason to believe the earlier ones were NOT 7/32-32.

Some Free Flight friends need to know, and I may be involved in helping them adapting 1.25" spinners (likely Brodak's 1/2A item) to their engines. I can measure the pitch and major diameter, but I don't have any these .15's, and the nearest one I know of is near Oregon City.  Steve

Hi from OZ Steve.  The thread on the .15 OS is either 7/32" x 32 UNS (nominal od 0.218" ) if you can get the taps or else a #12-32 UNEF. (nominal od 0.216")

[Tim Wescott]

Hi from OZ Steve.  The thread on the .15 OS is either 7/32" x 32 UNS (nominal od 0.218" ) if you can get the taps or else a #12-32 UNEF. (nominal od 0.216")

MSC Direct lists both sizes -- at the same low price of $40 each.

[Steve Helmick]

You're a machinist, Steve -- you could turn the thread without needing a tap 

Well....maybe. When I was young and worked for a large local aircraft factory, one night they gave me the task of turning up some microphone adapters, which for some silly reason (engineers, ya know!) had 1/4-60 threads. The adapters had to have internal threads, and I had to look through the shop's variety of antique lathes for one that would cut 60 TPI. And hand grind my own 60 degree internal threading tool from an internal grooving/parting tool. Fun? No, not so much!    Steve

[Dallas Hanna]

MSC Direct lists both sizes -- at the same low price of $40 each.

The #12-32 is reasonable on Fleabay US Tim.

Steve, if you can wait for the pony express mail I can send you a 7/32 UNS tap as I have a spare.  Let me know.

D

[Paul Allen]

Steve
         As Dallas said,I just checked a new in box OS 15 Max 111 and its 7/32-32 UNS.
Paul
In OZ

[Steve Helmick]

Thank Y'all for the information and links. I would appreciate it if somebody who has all three to test the MAX I, II and III all fit the same prop nut!

This is the 50th anniversary of the 1960 World FF Champs, where 10 F1C fliers were awarded "Equal 1st Place"! Our man Larry Conover used an OS Max (II?) in his Lucky Lindy, and two of my old FF buddies have built them, but can't find a 1.25" spinner to fit without some machine work. I've done some crazy stuff to fit spinners to my stunt engines, and may (or may not) get involved.    Steve

[Peter Roberts]

Steve,

Just checked.. it's the same prop nut for OS 15 MAX 1, 11 and 111.

[Steve Helmick]

Thank you all for the information!  Steve

[John Lindberg]

Bob? Mattes advertises on the NFFS website under "Community" I believe. He does a lot of work on OS 15's.