Ad selling chocks shows the same spurs and says- "A Sure Grip
In 1955 Aldon Co introduced cast steel chocks with the unique feature of replaceable spurs (or teeth). The spur is the key to effective rail wheel blocking. Under wheel pressure the spur bites into the hard, smooth surface of the rail to keep the chock from sliding. spurs and chock showing square and beveled ends
A Longer Useful Life
When the spur becomes dull from use it can be removed and turned to a fresh edge three times. You never have to throw an Aldon wheel chock away! When the spurs are used up, just order new ones at nominal cost and you’re back in business."
http://www.aldoninfo.com/chock-group/chocks.html