formwork nail

double-headed nail, scaffold nail, form nail

double-headed nail
A nail having two heads, one above the other; the upper head is driven with a hammer, and it is used to withdraw the nail; the lower head bears on the surface into which the nail is driven; used on temporary structures such as scaffolds, formwork, etc.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.