Core means having a rubber liner

A core device used in a moulding flask for making prefabricated concrete product, said device comprising

• a hollow tubular member formed from a rigid material and having an outer surface,
• a thin layer of rubber freely laid over the outer surface of said hollow tubular member,
• said thin layer of rubber having an outer surface for engaging and retaining concrete mixture poured into said moulding flask,
• said outer surface of the hollow tubular member being a truncated conical surface diverging toward the upper end of the tubular member,
• said thin layer of rubber having an inside surface which is a truncated conical surface diverging toward the upper end of the tubular member so as to mate with the outer surface of the hollow tubular member, and
• further said thin layer being secured at its upper edge portion to the top of the tubular member and having a bent portion protruding above the upper end of the tubular member, extending radially inwardly, and sloping downwardly to the upper edge portion of the thin layer of rubber.