As viewed from below the boom, the crank handle used on the 1949 through early 1961 wrecker was designed so the end link of the chain could be opened, passed through the hole in the crank handle and squeezed back together.

The crank handle as found on later 1961 forward Regular Series wreckers, does away with the hole and adds a welded smaller diameter wire through which the cord is placed and knotted to keep it from being pulled through.

The image below is a scan of the page in the 1961 Tonka dealer catalog featuring the #18 Wrecker. The chain is clearly visible and the wrecker desription references the chain. Original examples of the private label 1961 Standard Oil wrecker manufactured in 1961 have the cord. Thanks to Fred Carlton for sharing his wrecker knowledge.