The smaller .049 Cox engines all use a 5x40 thread screw or stud for the props. I need to check and see if a 5x40 screw is about the same size as the Mills engine crankshafts I have or not. I had not thought about trying a Cox 8x4 prop to see if it fit or not.
5x40 is about 1/8 inch size.

Images of three different propellers suitable for a Mills .75 engine, if you don't mind it being a little thirsty.

All are 7x4. An 8x4 is probably a better size for most applications.

Two, the Tornado and the Top Flite, are translucent white nylon. The Tornado was also commonly made in an opaque yellow nylon.

The surprise is the "dark horse" of the three. It's a JXF fibre propeller. Nicely made and balanced. It has a thin hub, the same width as the Top Filte propeller. Great performance, though liable to break in the event of an "arrival". It is available from HobbyKing and well priced.

i still have the tornado yellow nylon in 5x3, 5x4 and 6x3, left over from my initial fits for the dc dart

they do really well on the hobbyking c10 micro brushless 2900kv

pardon my hijack, but you've all given me a bad attack of nostalgia, so please excuse the slightly off-topic attached pics, which some of you will enjoy

for all their attraction, i have to confess diesels are nowhere near as practical as electric for this late convert to powered r/c

but the smell and sound are still wonderful when i fire them up

Originally Posted by scruffy1

pardon my hijack, but you've all given me a bad attack of nostalgia, so please excuse the slightly off-topic attached pics, which some of you will enjoy

No need to apologise scruffy, I sometimes fire up a diesel for no other reason than that it reminds me of the fun I had messing about with model planes when I was young.

Hahaa! I was flying a diesel (haven't owned a glow since 1968) one nice afternoon, whan I heard a great intake of air behind the model. I turned, and a gent with a UK accent smiled and said, "Ahhh!! Reminds me of my youth! Thank you very much!" and walked away...

Originally Posted by TLyttle

Hahaa! I was flying a diesel (haven't owned a glow since 1968) one nice afternoon, whan I heard a great intake of air behind the model. I turned, and a gent with a UK accent smiled and said, "Ahhh!! Reminds me of my youth! Thank you very much!" and walked away...

gotta confess my box also holds 2 cox .049's, an enya 2.5cc and an o.s. max 6cc - all glow plugs of course

except i haven't fired up a glowie since the late 70's - no fuel, battery or spares for the plugs

and i still have most of a 500ml bottle of still potent enough "pro-glow diesel"

My Mills .75 from posts 72 and 101 on the stand for it's first run since renovation.

Easy starting on my standard sports diesel brew.

First pic shows it being introduced to my "Millski". Boris, meet Nigel

Great job fiery, fantastic to see the engine running again

Lovely. It looks new. Terrific job done on the head.

Here is my "Millski" giving a sparkling performance on a classic white nylon Tornado 7x4.

The 10,500 rpm reading was not sustainable hot. Steady rpm's were mid to high 9,000's.

All..
I have written Hans at CS and he has sent me enough .075 parts to build a Mills inline twin. Has anybody measured the CS copy co I can verify my dimensions?
What I need are crankpin dia, shaft journal dia and stroke. Rather than hassle with a new block this is going to be a siamese with a modified rear case and a new design crank, (like the Sparey twin) so it's essentally 2 back to back cases with the snout cut off the rear casting and a threaded outer housing to tie them together in the threaded back plate area. CS also sent me an RC carby for a 1.3 for it, they have been very helpful and seem interested in our results.
Thanks
Al

Here is a video of what looks to be a home made flat twin, using first series "Boddo" Mills .75 top end parts.

It becomes over compressed as it warms up, add slows.

Boddo Mills Twin (2 min 8 sec)