In word formation, what is "U-bend ", "O-ring" & “S-tube” called?

[languefang]

In word formation, what is "U-bend ", "O-ring" & $B!H(BS-tube$B!I(B called?
Graphic words$B!)(BImage words$B!)(Biconic words$B!)(B Thank you. "X-ray" & "N-pole"
seems different, "X" and "N" are not about image. And what about
"pyramid"? It's about shape or form. But it's a little different.

 

[smallpond]

In word formation, what is "U-bend ", "O-ring" & $B!H(BS-tube$B!I(B called?
Graphic words$B!)(BImage words$B!)(Biconic words$B!)(B Thank you. "X-ray" & "N-pole"
seems different, "X" and "N" are not about image. And what about
"pyramid"? It's about shape or form. But it's a little different.

I think you posted to the wrong group but I would propose
"figurograph" from the Latin roots for shape and writing.
Pictograph or ideogram are the closest existing words in meaning.
Another example word would be "ell".

--S