M.D. Hubbard Spring Company - Since 1905 - Fourslide/Multislide Stampings, Wireforms, Torsion Springs, Extension Springs, Expansion Plugs, Ground Plugs Washers, metal Components

The counterbore should be round a free of tool chatter marks
The counterbore should be at least the depth of the thickness of the plug to be installed
For the best condition, the width of the bottom of the counterbore should be approximately equal to the thickness of the plug to be used.
The counterbore should be of a diameter that will take the plug without forcing, no larger. If forcing is required, the edge of the plug and the edge of the hole are apt to become marred, and leakage will occur.
The counterbore should be finished without any fillet. A fillet can prevent the proper seating of the plug. the counterboring tool should dwell long enough at the bottom of the counterbore to leave the bottom clean and smooth.
For best results, the angle between the cylindrical sides and the bottom of the counterbore should be 95 to 97 degrees. this allows the plug to turn inside out slightly, and then spring back to almost flat position. this gives maximum sealing quality.
If only a few plugs are to be installed, the best tool for setting them is a short piece of cold drawn shafting 8 or 10 inches long and of a diameter slightly less than the diameter of the plug to be set. By placing it perpendicularly over the plug, and striking the shafting one or two blows with a fairly heavy hammer, the plug can be set down sufficiently to not quite a flat position.

Installing Hubbard Expansion Plugs

M.D. Hubbard Spring Company
595 S. Lapeer Rd., Box 425T � Oxford, MI 48371
Ph: 248-628-2528 � Fax: 248-628-7734