Taking it that you are not growing a small variety then the problem is
due to the flowers not being polinated, this produces what we used to
call "chats". When you gut them open there is no pulp and no seed
inside.
David Hill

Well I never !
Never had a "chat" in all my years of growing many different tomato
varieties.
My pollination systems must be OK then.
I wonder if this possible with other fruits and vegetables.

Regards
Pete
www.thecanalshop.com