Gas tank vent line

[mike]

Hello everyone,

I finally decided to tidy up my engine bay and fabricate a missing gas tank vent tubing/re-route my gas lines. I searched all over the internet and couldnt find an answer for this. Does anyone know where to find the vent tube tee fitting that goes on the firewall (marked in red)? Part number is 178681 but I couldnt find it at any major military parts vendors websites. Also can you tell me what size thread are the end fittings on the tubing itself? I assume its UNF 3/8-20 for the 3/16 vent tube and UNF 1/2-20 for the 5/16 fuel lines?

thank you kindly for help
Mike

[Sundawg3]

Hey Mike,

One of the benefits of owning an aircraft parts business, (and paying thousands for manuals) is the ability to find information on items like you're looking for. See below for your answers on part number 178681:

Characteristic Specifications
MATERIAL COPPER ALLOY OVERALL
CONNECTION TYPE THREADED INTERNAL TUBE 1ST END THREADED EXTERNAL PIPE 2ND END THREADED INTERNAL TUBE 3RD END
CONNECTION STYLE B15A INVERTED FLARE 1ST END B67B PLAIN 2ND END B15A INVERTED FLARE 3RD END
SEAT ANGLE 42.0 DEGREES 1ST END 42.0 DEGREES 3RD END
NOMINAL OUTSIDE DIAMETER TUBE ACCOMMODATED 0.187 INCHES 1ST END 0.187 INCHES 3RD END
THREAD SERIES DESIGNATOR UNS 1ST END NPTF 2ND END UNF 3RD END
NOMINAL THREAD SIZE 0.375 INCHES 1ST END 0.125 INCHES 2ND END 0.375 INCHES 3RD END
THREAD QUANTITY PER INCH 24 1ST END
THREAD CLASS 3B 1ST END 3B 3RD END
LEG LENGTH 0.531 INCHES NOMINAL 1ST END 0.719 INCHES NOMINAL 2ND END 0.391 INCHES NOMINAL 3RD END
MANUFACTURERS CODE 21450
DEFINITIVE GOVERNMENT SPEC/STD REFERENCE 178681

[mike]

Hello Sundawg,

thank you for the details you provided. Do you know where I could get such a fitting? It seems to be non-existent at all the vendors websites. Also what exactly is a UNS thread? I can only find UNF thread end fittings for tubes. I wonder why they used two different thread styles for a connection of the same line.

regards,
Mike

[Sundawg3]

Mike,

A place called Orbital parts in Texas claims to have 11 under that part number and NSN or National Stock Number 4730-00-542-3205. You can try this email, rfq@orbitalparts.com, This is from an aircraft parts search I subscribe to. Keep in mind they are an aircraft parts reseller so don't have a heart attack when they quote you. Many will have a line item or PO minimum too. The lowest I've seen is $50.00 but many have a $200 or even $500.00 PO minimum. I've had to purchase all in stock to make a PO min in the past, but you will have an advantage no one else in the world does. You'll have the only in existence!!! Until the government has another auction and someone finds 1,000 in old bags in the bottom of a pile and puts them on eBay.

[rickf]

I might have one, I have a bunch of lines but the problem is they are in my storage container and that is in a lot that I am sure is flooded right about now with a lot more rain to come. It is a storage trailer so my stuff will be fine but getting to it will not be possible until next week at the earliest. Assuming the rain lets up.

[rickf]

Here is the government data for that fitting in case you are interested. I did not compare it with Sundawg's data, they may be the same.

Technical Data | NSN 4730-00-542-3205
Characteristic Specifications
MATERIAL COPPER ALLOY OVERALL
CONNECTION TYPE THREADED INTERNAL TUBE 1ST END THREADED EXTERNAL PIPE 2ND END THREADED INTERNAL TUBE 3RD END
CONNECTION STYLE B15A INVERTED FLARE 1ST END B67B PLAIN 2ND END B15A INVERTED FLARE 3RD END
SEAT ANGLE 42.0 DEGREES 1ST END 42.0 DEGREES 3RD END
NOMINAL OUTSIDE DIAMETER TUBE ACCOMMODATED 0.187 INCHES 1ST END 0.187 INCHES 3RD END
THREAD SERIES DESIGNATOR UNS 1ST END NPTF 2ND END UNF 3RD END
NOMINAL THREAD SIZE 0.375 INCHES 1ST END 0.125 INCHES 2ND END 0.375 INCHES 3RD END
THREAD QUANTITY PER INCH 24 1ST END
THREAD CLASS 3B 1ST END 3B 3RD END
LEG LENGTH 0.531 INCHES NOMINAL 1ST END 0.719 INCHES NOMINAL 2ND END 0.391 INCHES NOMINAL 3RD END
MANUFACTURERS CODE 21450
DEFINITIVE GOVERNMENT SPEC/STD REFERENCE 178681
Restrictions/Controls & Freight Information | NSN 4730-00-542-3205
Restrictions
Freight
Category Code Description
Shelf-Life Code: 0 Nondeteriorative
Hazardous Material Indicator Code N There is no data in the HMIS and the NSN is in an FSC not generally suspected of containing hazardous materials
Demilitarization Code: A Non-Munitions List Item/ Non-Strategic List Item - Demilitarization not required.
Controlled Inventory Item Code: U UNCLASSIFIED
Precious Metals Indicator Code: U Precious metal type is unknown
Criticality Code: X The item does not have a nuclear hardened feature or any other critical feature such as tolerance, fit restriction or application.