All Category - Hubbard Ground Expansion Plugs - Standard English Sizes

Standard English Sizes

  • The ground expansion plug offers the greatest level of holding power or leak resistance available in an expansion plug.
  • The ground edge provides maximum contact surface area and finest surface finish.
  • To maximize effect, the counter bore should receive special finishing.
  • Ground Plugs, installed in a correctly prepared counter bore, should eliminate the need for sealer and should hold highly penetrating liquids.
  • While their cost is higher than standard Hubbard Plugs, they are less expensive than pipe plugs or other closures when considering the total cost including tapping.
  • We grind the edge circumferentially to a high finish, and segregate the parts when packing to prevent damage to the edge during shipment. For greatest protection ground edge Hubbard Plugs should be kept in their packing containers up to the point of assembly.
  • We have found 1” diameter .083” thick steel ground plugs to hold 1,600 lbs of pressure before failure, which is between 10 and 20 times the holding power of a standard blanked edge plugs. The effective use range should be less than that.

Stock Materials:

  • Steel: SAE1008/1010 low carbon steel: ASTM#A109 or A569 depending on gage.
  • Stainless Steel: 302 / 304 ASTM#A313
  • Brass: ASTM#B36.
* These are materials we stock in various thicknesses. It does not mean we have finished inventory of all plugs in each of these materials.
** Customer specific materials different than those listed above are commonly run.


  • All ground plugs are packaged in segregated rows with a special light oil finish.

Item #
Nominal Diameter 'A' Fraction
Nominal Diameter 'A' Decimal
Maximum Diameter Limit
Minimum Diameter Limit
Spherical Radius
Note : click on item number to submit request for quote
HPG-625 5/80.6250.6280.6223/4
HPG-685 .685.6850.6880.6827/8
HPG-750 3/40.750.7530.74715/16
HPG-875 7/80.8750.8780.8721-3/32
HPG-937 15/160.9370.940.9341-5/32
HPG-1000 111.0030.9971-1/8
HPG-1123 1-1/81.1251.1281.1221-3/8
HPG-1155 1.1551.1551.1571.1511-1/2
HPG-1168 1.1681.1681.1711.1651-1/2
HPG-1187 1-3/161.1871.191.1841-1/2
HPG-1250 1-1/41.251.2531.2471-5/8
HPG-1363 1.3631.3631.3661.361-13/16
HPG-1375 1-3/81.3751.381.371-13/16
HPG-1437 1-7/161.4371.4421.4322
HPG-1492 1.4921.4921.4971.4872-1/8
HPG-1500 1-1/21.51.5051.4952-1/8
HPG-1625 1-5/81.6251.631.622-3/8
HPG-1739 1.7391.7391.7441.7342-11/16
HPG-1750 1-3/41.751.7551.7452-11/16
HPG-1875 1-7/81.8751.881.873-3/16
HPG-1921 1-59/641.9211.9261.9163-3/32
HPG-1937 1-15/161.9371.9421.9323-3/32
HPG-2000 222.0051.9953-3/16
HPG-2062 2-1/162.0622.0672.0573-1/4
HPG-2125 2-1/82.1252.132.123-1/4
HPG-2250 2-1/42.252.2552.2453-9/16
HPG-2375 2-3/82.3752.382.373-7/8
HPG-2500 2-1/22.52.5052.4954-5/32
HPG-2625 2-5/82.6252.632.624-1/4
Total: 29