Drill mountable drill guide

A drill chuck guide for retaining a instrument, comprising:

• a threaded outer segment having an axially aligned bore for receiving said instrument theretrough;
• a threaded inner segment that is adjustably screwed into said threaded outer segment to adjust the length of said bore between fully extended and fully retracted positions, so as to expose a preselected length of said instrument, wherein only said preselected length of said instrument penetrates into a material to be drilled;
• and
• a hollow tube having first and second ends, wherein at least said first end having a lip, said hollow tube dimensioned for insertion into said bore for securing and receiving at said lip end said instrument therethrough, wherein the length of said lip to the other end of said hollow tube being less than or equal to the length of said inner and outer segments in said fully retracted position.

A drill guide for restricting the penetration depth of an instrument, comprising:

• an adjustable length sleeve comprising,
• an outer segment having a first longitudinal bore, and
• an inner segment having a second longitudinal bore, and being retractably disposed within and protruding from only a first end of said first bore, and so that a displacement of said inner segment out of and into said first bore changes a longitudinal length of said adjustable length sleeve, so as to expose a preselected length of said instrument,
• wherein said penetration depth of said instrument is restricted to said preselected length, and
• wherein said adjustable sleeve further comprises a spring for biasing said inner segment into an extended position from said outer segment.