I’ve been googling for a whole 20 mins and can’t find out – I’m referring to the plastic underside which the rails connect with – I’ve always called it the carcass or the undercarriage? Be grateful if anyone knows the correct term ?

Thrunge.

Chassis?

Base?

Cockpit.

It’s the shell.

It’s called the Hull.

Carcass would seem as good a name as any. Perhaps there is not an offical / agreed name

Fairy Hammock

Eranu

Shatners bassoon.

They wanted to call it a Kuku Penthouse, but that was already taken.

Lower flange gusset

Carcass? Shell? Body? Support? All would make some sort of sense to me…

I’m Assuming you are talking about a plastic or carbon jobbie with foam and a cover on top…

Frame, innit?
Is on leather ones anyway.

The Dark Side.

the really muddy bit

Gooch basket

😆 at the above posts but there is one correct one hiding in there, it is indeed known as the hull.

there is one correct one hiding in there, it is indeed known as the thrunge.

FTFY

Hull

I’ve always called it the carcass – but shell is probably the more generic name thinking about it ..

Gouch

Hod

Its the saddle surely?

The saddle assembly comprises of the saddle (the padded plastic bit) and the rails which are the means by which the saddle is mounted to the clamp on top the seat post or seat pin?

And the padded plastic bit is made up of parts too.
Padding, hull and cover is what I know them as.

Saddle = rails, hull, padding and cover

Hull,no doubt.

Saddleguts