The word "putlock" is actually a variation of "putlog", which is an architectural term for a horizontal timber beam commonly used in scaffolding. The spelling "putlock" may seem unusual because it specifies the pronunciation of the "u" as /ʌ/, unlike in words like "but" where the same letter is pronounced as /ʊ/. The IPA phonetic transcription for "putlock" is /ˈpʌtlək/, with the stress on the first syllable and the final sound represented as "-lək".
One of the pieces of timber, about 7 feet long, used in building scaffolds, one end of which is inserted into the wall, and the other fastened to one of the upright poles, forming the skeleton of the scaffold.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.