with which aluminum is deformed, it is necessary to distribute screw and nut pressure by means of plain washers. 

Hardware used to make bonding or grounding connections should be selected on the basis of mechanical strength, current to be carried, and ease of installation. If connection is made by aluminum or copper jumpers to the structure of a dissimilar material, a washer of suitable material should be installed between the dissimilar metals so that any corrosion occurs on the washer. 

Hardware material and finish should be selected on the basis of the material of the structure to which attachment is made and on the material of the jumper and terminal specified for the bonding or grounding connection. Either a screw or bolt of the proper size for the specified jumper terminal should be used. When repairing or replacing existing bonding or grounding connections, the same type of hardware used in the original connection should always be used. 

## Connectors 

Connectors (plugs and receptacles) facilitate maintenance when frequent disconnection is required. Since the cable is soldered to the connector inserts, the joints should be individually installed and the cable bundle firmly supported to avoid damage by vibration. Connectors have been particularly vulnerable to corrosion in the past, due to condensation within the shell. Special connectors with waterproof features have been developed that may replace nonwaterproof plugs in areas where moisture causes a problem. A connector of the same basic type and design should be used when replacing a connector. Connectors that are susceptible to corrosion difficulties may be treated with a chemically inert waterproof jelly. When replacing connector assemblies, the socket-type insert should be used on the half that is “ live” or “hot” after the connector is disconnected to prevent unintentional grounding. 

## Types of Connectors 

Connectors are identified by Air Force Navy (AN) numbers and are divided into classes with the manufacturer’s variations in each class. The manufacturer’s variations are differences in appearance and in the method of meeting a specification. Some commonly used connectors are shown in Figure 4-115 . There are five basic classes of AN connectors used in most aircraft. Each class of connector has slightly different construction characteristics. Classes A, B, C, and D are made of aluminum, and class K is made of steel. 

1. Class A—solid, one-piece back shell general-purpose connector. 

2. Class B—connector back shell separates into two parts lengthwise. Used primarily where it is important that the soldered connectors are readily accessible. The back shell is held together by a threaded ring or by screws. 

3. Class C—a pressurized connector with inserts that are not removable. Similar to a class A connector in appearance, but the inside sealing arrangement is sometimes different. It is used on walls or bulkheads of pressurized equipment. 

4. Class D—moisture and vibration resistant connector that has a sealing grommet in the back shell. Wires are threaded through tight fitting holes in the grommet, sealing against moisture. 

5. Class K—a fireproof connector used in areas where it is vital that the electric current is not interrupted, even though the connector may be exposed to continuous open flame. Wires are crimped to the pin or socket contacts and the shells are made of steel. This class of connector is normally longer than other connectors. 

## Connector Identification 

Code letters and numbers are marked on the coupling ring or shell to identify a connector. This code provides all the information necessary to obtain the correct replacement for a defective or damaged part. [Figure 4-116] 

Many special-purpose connectors have been designed for use in aircraft applications. These include subminiature and rectangular shell connectors, and connectors with short body shells, or of split-shell construction. 

## Installation of Connectors 

The following procedures outline one recommended method of assembling connectors to receptacles: 

1. Locate the proper position of the plug in relation to the receptacle by aligning the key of one part with the groove or keyway of the other part. 

2. Start the plug into the receptacle with a slight forward pressure and engage the threads of the coupling ring and receptacle. 

3. Alternately push in the plug and tighten the coupling ring until the plug is completely seated. 

4. Use connector pliers to tighten coupling rings one- sixteenth to one-eighth turn beyond finger tight if space around the connector is too small to obtain a good finger grip. 

