Fastening in series (6)
I believe the answer is:
string
This could be a double definition.
'fastening' is the first definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'series' is the second definition.
(sequence of similar items or events)
'in' acts as a link.
Can you help me to learn more?
(Other definitions for string that I've seen before include "Row" , "Group of racers" , "A - - of Pearls" , "How long could a piece of it be?" , "groups of horses" .)