Whilst I am loathe to contradict you Graham, the yellow connector certainly look like a standard patch lead that has been pushed onto the threads. You can even see the threads through the expansion gaps, as indicated.
I see no sign of any adapter.
In fact, the adapter you suggest wouldn't be required as the amp is threaded thereby not needing the coax to be converted.
artflow_201808101508.jpg (272.7 KB, 2 downloads) 5 years old SSThing - 14 minutes ago »
Whilst I am loathe to contradict you Graham, the yellow connector certainly look like a standard patch lead that has been pushed onto the threads. You can even see the threads through the expansion gaps, as indicated.
I see no sign of any adapter.
In fact, the adapter you suggest wouldn't be required as the amp is threaded thereby not needing the coax to be converted.
I don't see how a Belling-Lee could possibly fit. The hole in a F socket is tiny. If you are correct it certainly is a bodge.
One of these with a short length of coax with a f connector on each end will convert it unless the Belling Lee is completely ruined.
http://cpc.farnell.com/pro-signal/rw7-011/tv-coax-socket-to-f-female-brass/dp/CN16115?mckv=sw5mVutv3_dc|pcrid|224689766569|kword||match||plid||slid||product|CN16115|pgrid|49729733449|ptaid|pla-412324023826|&CMP=KNC-GUK-CPC-SHOPPING&gclid=EAIaIQobChMI7-Ww7dri3AIV6rXtCh1mfg-YEAQYASABEgIcufD_BwE
It is probably THIS {Click} sort of thing.
I didn't know they existed either.
As GLT says, a Belling Lee would just not fit.
Trev - 4 minutes ago »
It is probably THIS {Click} sort of thing.
I didn't know they existed either.
As GLT says, a Belling Lee would just not fit.
Well found!!
That certainly looks like the one, expansion slots etc all appear the same.
Just out of curiosity, I have just (without much effort) successfully pushed a male standard fitting onto an f-connection and it's a very flush fit externally but I suspect the inner of the f has been damaged/distorted. A standard female would be impossible without a definite bodge 
Trev - 17 minutes ago »
It is probably THIS {Click} sort of thing.
I didn't know they existed either.
As GLT says, a Belling Lee would just not fit.
Never seen one either but a search found this
The reviews make interesting reading. 
I have in the past used a F to male belling lee and a f to female to make a quick disconnect option on a satellite cable I needed to disconnect fairly often. This had no noticeable effect with signal quality and strength remaining at 100%.
This is why forums such as here are invaluable. Through the combination of (vast) knowledge and perseverance of the collective, the answers are found.
Here's the ones I was referring to in #8...
Pollensa1946 - 25 minutes ago »
Here's the ones I was referring to in #8...
https://blusas.co.uk/mho.php?loc=https://www.amazon.co.uk/Plug-Socket-Female-Adaptor-electrosmart%C2%AE/dp/B003894IVM&tag=blusas008-21
Both male and female versions are linked to in post 10. What none of us knew about was the quick release F connector that dispenses with the screw on 11mm nut.
Generally female plugs are used for output with male for input.
eg
A PVR to TV Belling Lee has a female plug for a pvr out to a male for TV in (patch cord)
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