new kitchen tap trouble to install

[t3rm3y]

our old tap was knackered, we may upgrade kitchen soon so opted to buy a cheap tap to get us buy as emergency fix.
Its a monobloc tap to replace one.
Got the old one off, but cannot install the new one
We have a hole in the sink side board (i assume this is standard, and it doesnt go through the worktop itself?) but i have found that the steel washer on the underside of the sink does not go on due to the flexi pipes appearing to be too wide.
i attached the flexi pipes, dropped them through the hole and then try to put the steel plate against underside of the sink but it wont go in the right place as the fatter part of the flexi pipe connectors appears ot block it, so in turn means i cant screw the threaded bar on.
i cant believe they would sell something that doesnt physically work , so am i missing something? if the sink was thicker then the steel washer would miss the flexi pipe connecting bits and would fit. (hope i make sense).
There was a plastic item that came with the pack, not sure if this should be used somewhere? but it could just be to mark out the size of the hole to cut if a new install??
ill see if can add pictures to try to explain

 

[t3rm3y]

 

[t3rm3y]

 

[Newboy]

The random plastic part is a brace - it fits between the underside of the sink and the backplate.

 

[t3rm3y]

thanks newboy, any idea which way round it goes? as the round bit protrudes out, but is too large for the hole in the sink worktop, os does the flat bit sit against the underside of the sink, and the circular part points downwards and my backplate and rubber part press against this? doesnt sound like the tightest fit, the old tap was solid. not so sure about htis one..

 

[Newboy]

Flat base against the underside of the sink with the washer between, backnut against the cylinder part.