Now that you've read about what MIL-SPEC means, how do you choose the right one for your project? Well the first thing we need to do is understand how the part numbers work and what they mean. For this post, we will be referring to the most popular MIL-SPEC connector we sell: MS3476A22-55P
To make this as simple as possible, let's break this part number into 6 smaller parts so we can understand what each one is telling us.
- SHELL TYPE
- SHELL SIZE
- CONTACT LAYOUT (aka ARRANGEMENT)
- CONTACT TYPE
SERIES - MS3476A22-55P
The series is the type of connector the part number is. In this case "MS" stands for Military Standard, or as we've already learned in the last blog post - MIL-STD.
SHELL TYPE - MS3476A22-55P
The shell type is broken down into several different potential configurations, especially depending on the size of connector, series of connector etc. The connectors that we offer are commonly broken out into 3 different types:
3470 - Square Flange Receptacle (chassis side) -
The 3470 is a flanged connector with 4 holes in the flange for simple mounting. Each connector page shows dimensions for the holes that are required to be drilled for mounting.
3474 - Jam Nut Receptacle (chassis side) -
The 3474 is another commonly used connector type, where all that's required is to drill the hole for the connector, and a jam nut secures it to your firewall or mounting surface. Each connector page shows the dimension for the hole that is required to be drilled for mounting.
3476 - Plug (harness side) -
The 3476 is the mating side to both the 3470 and 3474 that goes on the opposite end of the harness. A 3470 and 3474 connector will not mate!!!
Other shell types include MS3471 (cable connecting receptacle) MS3472 (wall mount wide flange) MS3475 (plug with RFI ground fingers) and more. We do not typically stock these for use with automotive based customers. We do use some of these for our defense clients, and you will see them on occasion in our clearance section or even in the MIL-SPEC connectors section.
CLASS / PLATING - MS3476A22-55P
As discussed in our previous blog article, we offer primarily black zinc nickel as our finish of choice. It's compatible with ALL other finishes available on these connectors, and is tied with olive cadmium for the best corrosion resistance amongst the finishes. This is signified with the letter "A". For those of you who chose nickel finish, you will likely see the letter "L", and for those who choose olive drab green cadmium those carry the "W" finish code.
SHELL SIZE - MS3476A22-55P
This is simply the size of the connector and isn't relevant aside from making sure the mate is the same shell size, and the backshell you pick will also fit it.
CONTACT LAYOUT (ARRANGEMENT) - MS3476A22-55P
This is where we get the most questions. In our example, the contact layout is "55". In this instance, the number 55 also happens to be the number of terminals the connector has. That is NOT ALWAYS THE CASE! For example, an 8-33 does not have 33 terminals in it, it has 3. Another example is an 8-98 which does not have 98 terminals it also has 3. So, make sure you read the connector description to find out not only how many contacts the connector has, but how many of what wire gauge too. We offer a contact layout PDF on the main MIL-SPEC connector page which we'll link below.
CONTACT TYPE - MS3476A22-55P
Finally is the orientation of the terminals for the connector. This is simply a P for PINS or an S for SOCKETS. Pins are male, sockets are a female terminal. As with all connectors, you discuss a connectors orientation based on the terminals in it, not the connector shell. So, if you ask someone for a male MILSPEC connector, then you will be asking for a connector with male PINS.
When designing your harness, it's common to use socket connectors on bulkheads and pin connectors on the harness side to help prevent damage to the terminals when the harness is not in the vehicle. The sockets are much better protected with unhooked from its mate. It's always recommended to use protective caps for your connectors when they are not plugged into their mates. This prevents terminal damage and any foreign debris from entering the connector.
So if we refer back to our sample part number, MS3476A22-55P we are looking at a MIL-SPEC connector, plug side, black zinc nickel finish, shell size 22, contact layout 55 with pins. This is what the connector looks like that we have just deciphered:
Now, there is one last part we need to discuss. If you look at the photo above, you'll see that there are threads on the bottom of the connector. These are for the backshell to thread onto. The backshell is used as a safe area to protect strain reliefs, also referred to as service loops. These are loops in the wire at the connector so that the connector can be serviced later if needed, and a contact removed from the connector easier than if it there was no slack of wire at the connector. This is also where you epoxy the formed boot to the connector to seal it from the elements. You can use all the heat shrink, and proper connectors with the best wire money can buy, but if you allow moisture or dirt to penetrate your harness, you will just be asking for problems long term. We will cover what that means in detail, including covering Tyco System 25 and WHMA/IPC-620A later.
See our full range of MIL-SPEC connectors here -MIL-SPEC CONNECTORS