If you are a technician, you might be referring to a hardware dongle used to force Samsung devices into "Download Mode" or perform UART servicing.
Essential for repair shops dealing with older Samsung devices (S4, S5, Note 3 era). Obsolete for modern smartphone repair. samsung 350k tool
The "350k" resistance tool (often a small USB jig or adapter) is used to ground a specific pin on the micro-USB port to manually force the phone into Download Mode. If you are a technician, you might be