I just made a large order with Paul zhang, the response time has been very quick usually replying in under an hour, payment was made at the start of the month and I have already receive most my order, the rest should be here on Monday.
the 18mm connectors are a standard m18x1.5 thread so i would think the 13.5mm would be would be close to a m14x1.5 or m14x1.25, the issue would be finding a jam nut (thin nut) in that size