Model’s tall, showing bit of leg (5)
I believe the answer is:
thigh
'bit of leg' is the definition.
('thigh' is part of 'leg')
'model's tall' is the wordplay.
'model' becomes 't' (Ford Model T car).
'tall' becomes 'high' (similar in meaning).
't'+'high'='THIGH'
'showing' is the link.
(Other definitions for thigh that I've seen before include "Joint of meat" , "part of body" , "top of pin" , "This bone is the femur" , "Leg between knee and hip" .)