Jagwire of all things cables makes such a cable stop. Their part # is BOT115-6. I got mine from QBP in a 100 piece bottle. The OD of the part that goes into the diver's helmet is just under 4mm and the ID of the hole the cable goes into is 5mm. Send me your street address and I'll mail you a couple. Or if you prefer you can pick them up yourself when you come to take my framebuilding class
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