Abstract: Improved wellhead structure and method for modification of commercially operating wellheads. Screwed type wellheads include an adapter attached to a body extending upwardly from a well bore. The adapter supports a stripper rubber and a slip assembly on internal shoulders. An upper shoulder supporting the slip assembly and a lower shoulder supporting the stripper rubber extend radially into the central bore of the adapter a selected distance allowing unencumbered removal and reinsertion of the stripper rubber through the top portion of the adapter while the adapter is affixed to the body. Barrels radially extending from the adapter wall contain hold down screws extendable into the bore to selectively restrict upward motion of the stripper rubber.