Review on TENINYU RJ9 4P4C 4 Conductor Straight Modular Telephone Data Extension Flat Cord Cable Silver 7FT 2PACK: Reliable Connectivity for Phone and Data Transmission by Ashley Grant

At first both cables did not work, then they worked sporadically while I was pulling the plugs into the mating sockets. As a result, I looked at the connectors on these cables under the microscope and found that all 4 connectors (2 on each cable) in the recess under one of the contacts (pin 1, black cable) are damaged - either the mold is bad, or they were hooked up to a bad test fixture during production. The damage was so severe that on 3 of the 4 terminals a piece of plastic was partially cut and bent, covering part of the contact and thereby blocking the electrical connection. Xacto knife to remove the piece of plastic and scrape off the damaged area, but that would be difficult without a microscope. Don't buy them if you don't have a microscope and don't want to fix connectors. The seller should check their inventory.