All three of these come in 76MM and 60MM. Both the Adjustable and Powermatic Adjustable come with a 76MM Column on the bottom and a 60MM Column on the top that slides into the bottom column.
All columns are tapered on the bottom. Adjustable and Powermatic Adjustable columns tapered on one end will be identified by a –1 at the end of the part number. Some columns are also tapered on the top. The ones that are tapered on the top require using a standard base on the top as a support. The Adjustable and Powermatic Adjustable columns tapered on both top and bottom will be identified by a –2 at the end of the part number.
Adjustable and Powermatic Columns for Tables are adjusted by the clamping knob.
Adjustable and Powermatic Columns for Helm Chairs are adjusted by a release lever.
Q: When must I use a through the floor model?
A: When looking for an Adjustable or Powermatic Adjustable column that adjusts to a very low position while still extending to 30 inches or so, you will likely need to use a through the floor column.
Q: When is a column tapered on both ends used?
A: These are often use when it supports a small round table top, or when the standard table support is too big for the tabletop.