Clamping apparatus for holding a toolholder shank

An apparatus for releasably holding the tubular shank of a toolholder, said apparatus comprising:

• a tool support member having a forwardly facing surface and bore intersecting said forwardly facing surface and extending rearwardly therefrom for receiving said shank;
• a first clamping jaw and a second clamping jaw mounted in said tool support member and extending at least partially into said bore;
• a means for reciprocating said first and said second clamping jaws radially inwardly for being receivable at least partially within said tubular shank and radially outwardly for clamping said tubular shank to said tool support member;
• said means for receiprocating including a threaded member radially extending into said first and said second clamping jaws for reciprocating said first and second clamping jaws;
• and said threaded member including a first threaded diameter threaded in a first direction at a first pitch and threadably engaged in said first clamping jaw, and a second threaded diameter threaded in said first direction at a second pitch and threadedly engaged in said second clamping jaw.