Voltage rating on panel jack
6.3V isn't the physical rating of the plug, but the regulatory rating. 4mm OD × 1.7mm ID is type EIAJ-02, part of a series of sizes of barrel connector intended to provide some correlation between plug dimensions and voltage. Type 02 is for voltages between 3.15V and 6.3V, but likely would work with higher voltages.

Given that the connector itself is intended not to be used with anything above 6.3V in order to prevent damaging devices (from plugging in the wrong voltage connector), I wouldn't recommend using this connector for this purpose.