Hubbard (Welch Type) Expansion Plugs – Brass

“d” Hole = Plug upper limit +.002”, more clearance may be needed for plugs over 2.5”.

Depth = 1-1/2 to 2 material thicknesses (1 material thickness minimum).

Shoulder = 1 material thickness

1. The counter bore should be of a diameter that will take the plug without forcing, no larger. Typically this means .002” larger than the maximum plug diameter, although more clearance than .002” should be given to larger diameter plugs. If the plug is forced or press fit in the hole prior to expansion, the edge of the plug and the edge of the hole are apt to become marred, and leakage will occur.
2. The counter bore should be round and free of tool chatter marks. 100 micro inches or smoother is a good finish guideline.
3. The counter bore should be finished without any fillet. A fillet can prevent the proper seating of the plug. The counter boring tool should dwell long enough at the bottom of the counter bore to leave the bottom clean and smooth. The sharper the corner, the better the seal.
4. The counter bore should be at least the depth of the material thickness of the plug to be installed.
5. For the best condition, the width of the bottom of the counter bore should be approximately equal to the thickness of the plug to be used.
6. For best results, the angle between the cylindrical sides and the bottom of the counter bore should be 95 to 97 degrees. This allows the plug to turn inside out slightly, and then spring back to an almost flat position – providing maximum sealing quality.

NOTE: The above hole configurations are for optimal sealing. Flat bottomed counter bores with varying shoulder widths are used for general sealing – applications with no liquid retention or pressure requirements.