The adapter you have is specific to CVHS (VHS-C, compact vhs) tapes, it is not built for 8mm tapes.
In fact, there is unfortunately not a direct adapter for 8mm, which can't be read by the head of a VHS system.
Now, there may be some (used) options for a HI8 player, which is essentially a mini vcr to play back your hi8 tapes.
Even those though are very difficult to find, and quite expensive due to the age/obsolescence and low supply.
Your best long-term option, if you have a collection of those tapes, would be to play them back in the camcorder or original recording device, via video capture device, and using that to archive the content onto a computer for transfer or storage to hard drive or dvd. Would you be interested in equipment to do that?
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