Connects about 50 slabs (5)
I believe the answer is:
tiles
'slabs' is the definition.
(I know this)
'connects about 50' is the wordplay.
'connects' becomes 'ties' ('tie' can be a synonym of 'connect').
'about' is an insertion indicator.
'50' becomes 'l' (Roman numeral).
'ties' going around 'l' is 'TILES'.
(Other definitions for tiles that I've seen before include "Roofing materials" , "Small oblong slabs used in roofing" , "Glazed rectangles used to cover walls or floors" , "Thin flat slabs of fired clay" , "Thin flat slabs, for roofing perhaps" .)