Hugh,
I have the same tester in the garage, iam sure it is a rubber cone that you push into the plug hole - i will try get you a photo.
There will be a local snap on rep to you, ask your friendly local garage for info - they probably have an account and parts can be sourced.
similar to whats on the end of this - https://www.ebay.com/itm/175589714508
I have the same tester in the garage, iam sure it is a rubber cone that you push into the plug hole - i will try get you a photo.
There will be a local snap on rep to you, ask your friendly local garage for info - they probably have an account and parts can be sourced.
similar to whats on the end of this - https://www.ebay.com/itm/175589714508