Dell part number J5G42 (often listed as 0J5G42) is a Power Switch Cable Assembly designed specifically for the Dell Precision T1700 Small Form Factor (SFF) workstation. 

Compatibility:
Dell Precision T1700 (SFF/Small Form Factor): This is the primary system for this part.
Form Factor Note: This part is designed for the SFF chassis and may not be compatible with the Mini-Tower (MT) version of the T1700. 

It is used to connect the front power button to the motherboard.