Expansion Plugs

Expansion plugs are an inexpensive and effective way to seal holes in a wide range of metal products.
Expansion plugs provide a metal-to-metal seal with performance characteristics detailed below.
The classic use case is sealing core holes in machined castings.
We manufacture all our expansion plugs at our facility in Oxford, Michigan, USA.

Hubbard Spring is the original patent holder and manufacturer of expansion plugs since 1913.

Cup Plugs

Cup Plugs – burnished edge ENGLISH spring lock

Cup Plugs – burnished edge METRIC DIN443

Cup Plugs – burnished edge FORD WM104 + WM901

Burnished edge Cup Plugs are engineered to seal holes ranging from [8mm - 40mm] and [0.312” - 2.250”].
High-pressure retention combined with simple hole preparation and installation.
Cup plugs have the least overall cost of all expansion plugs when considering hole preparation and installation.

SEALING DYNAMICS

The seal is created by the tapered and burnished sealing surface compressed into a machined through hole.
Retains up to 60 bar pressure on 25mm or 1” diameter plugs.
Requires a machined through hole with lead-in as detailed above and on the part print available on the item page.
Requires a shouldered installation tool as detailed above and on the part print available on the item page.

Cup Plugs – burnished edge PRECISION series

Precision series Cup Plugs are engineered to seal holes ranging from [3mm - 8mm] and [0.118” - 0.312”].
Good-pressure retention combined with simple hole preparation and installation.
Cup plugs have the least overall cost of all expansion plugs when considering hole preparation and installation.

SEALING DYNAMICS

The seal is created by the tapered and burnished sealing surface compressed into a machined through hole.
Retains up to 30 bar pressure on 6mm or 1/4” diameter plugs.
Requires a machined through hole with lead-in as detailed above and on the part print available on the item page.
Requires a shouldered installation tool as detailed above and on the part print available on the item page.

Welch Plugs – blanked edge ENGLISH

Welch Plugs – blanked edge METRIC DIN470

Blanked edge Welch Plugs are engineered to seal holes ranging from [3mm - 100mm] and [0.125” - 4.500”].
Good for limited depth and low-pressure applications.
Best used as cover or to retain liquid at low or no pressure.
Blanked edge Welch Plugs are the least expensive expansion plug but require a machined counterbore.

SEALING DYNAMICS

The seal is created by the sharp corner of the blanked edge expanding into the sharp corner of the counterbore wall.
Retains up to 3 bar pressure on 25mm or 1” diameter plugs.
Requires a machined counter bore as detailed above and on the part print available on the item page.
Requires an installation tool as detailed above and on the part print available on the item page.

Welch Plugs – ground edge ENGLISH

Welch Plugs – ground edge METRIC DIN470

Ground edge Welch Plugs are engineered to seal holes ranging from [8mm - 63mm] and [0.312” - 2.500”].
Good for limited depth and high-pressure applications.
Meet or exceed the pressure retention of cup plugs.
Ground edge Welch Plugs are usually more expensive than cup plugs and require a machined counterbore.

SEALING DYNAMICS

The seal is created by the sharp corner of the ground edge expanding into the sharp corner of the counterbore wall.
Retains up to 100 bar pressure on 25mm or 1” diameter plugs.
Requires a machined counter bore as detailed above and on the part print available on the item page.
Requires an installation tool as detailed above and on the part print available on the item page.