Extra Extended Fuel Tank .049

Best to proceed as follows to use tank extender kit:
a- have confirmed good running engine
b- assemble with RTV sealant on all seams
c- use RTV on Q-tip fiber to seat head of fillister screws

And be mindful of weight and balance changes.

Thanks for information. Where are very long fillister screws available?

Iceberg wrote:Thanks for information. Where are very long fillister screws available?

These are hard to find. Amazon has up to 1 1/4". Longer seem to be unobtanium.

https://www.amazon.com/Stainless-Machine-Fillister-Slotted-Threads/dp/B000FN1WAY/ref=sr_1_fkmr1_4?ie=UTF8&qid=1543705841&sr=8-4-fkmr1&keywords=2-56+fillister+head+1+1%2F2

McMaster Carr has 2-56 socket head screws up to 2 1/2".
The heads do fit Cox backplates.
https://www.mcmaster.com/standard-socket-head-screws
Looking at the prices for 1 1/2", I don't know where I got
the ones I have. Certainly didn't pay $2.70 a piece.
Bob

dckrsn wrote:McMaster Carr has 2-56 socket head screws up to 2 1/2". The heads do fit Cox backplates.
https://www.mcmaster.com/standard-socket-head-screws
Looking at the prices for 1 1/2", I don't know where I got the ones I have. Certainly didn't pay $2.70 a piece.

I had to right click on the link and open it up in a separate window to view specs, (otherwise the line drops down with how many you want to order), but here is why:

Black-Oxide Alloy Steel Socket Head Screw
2-56 Thread Size, 1-1/2" Long
McMaster SKU# 91251A200

McMaster wrote:With a tensile strength of 170,000 psi, these alloy steel screws are stronger than Grade 8 steel screws. Length is measured from under the head. Black-oxide steel screws are mildly corrosion resistant in dry environments. Coarse threads are the industry standard; choose these screws if you don’t know the pitch or threads per inch. Screws that meet ASTM A574, ASTM A574M, and ISO 898-1 comply with specifications and testing requirements for material quality.

The OEM screws we normally use for model engine use are softer, under Grade 5, may be even a Grade 2 or 3. That is why it is easy to bugger the heads. That price includes the amount of testing required to certify them. Doesn't say, but these screws seem they may be suitable for use in aircraft. Anyway, that is my impression.

These are a little cheaper, at least you get 10 for $7.25:
Microfasteners SKU# SCA0224, 2-56 x 1-1/2 socket head cap screw alloy steel

I'm sure one can find a better price if they look around.