Positive engagement screw driver tool

A screwdriver tool provides positive engagement with screw having a head with a straight slot. An end portion is substantially flat, but is wider at its midpoint than at its ends. A tapering segment extends from the end portion and an engagement area is defined on the side of the segment. Engagement initially occurs at a location intermediate to the ends and midpoint of the end portion. As torque on the screwdriver is increased the engagement extends toward the midpoint and up the side of the segment.

BACKGROUND OF THE INVENTION 
This invention relates in general to tools for use with fastening devices 
and, in particular, to a tool which mates in positive engagement with the 
fastening device. 
Prior art tools for use with screws having a head with a straight slot have 
an end which generally mates with the screw. The ends of these tools or 
screwdrivers, as they are commonly known, are tapered so that they easily 
fit into the slot or other recessed configuration in the screw head. A 
problem with these screwdrivers is that if the screw is very tight in some 
object, it may require a high degree of torque to remove the screw. Very 
often the head of the screw is damaged if the screwdriver slips when 
attempting to remove the screw. This can easily occur because the end of 
the screwdriver is not designed to fit perfectly into the recess or slot 
in the head of the screw. 
The presentation invention overcomes this problem in the prior art. 
SUMMARY OF THE INVENTION 
The present invention is a screwdriver tool which provides positive 
engagement with screws having a head with a straight slot. An end portion 
is substantially flat, but is wider at its midpoint than at its ends. A 
tapering segment extends from the end portion and an engagement area is 
defined on the side of the segment. Engagement initially occurs at a 
location intermediate to the ends and midpoint of the end portion. As 
torque on the screwdriver is increased the engagement extends toward the 
midpoint and up the side of the segment. 
OBJECTS OF THE INVENTION 
It is the primary object of the present invention to provide an improved 
tool capable of positive engagement with a fastening device. 
It is a secondary object of the present invention to provide an improved 
tool which prevents damage to the fastening device.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention provides a solution to a problem in the prior art 
which has existed for a long time. When a prior art screwdriver, such as 
the one shown in FIG. 1, is used with a screw of the type shown in FIG. 2, 
there is a possibility that the screwdriver may slip and damage the head 
of the screw. This occurs because the end 10 of the prior art screwdriver 
12 is tapered and does not fit perfectly in the slot 14 in the head 16 of 
the screw 18. The engagement of the screwdriver 12 and the screw 18 is 
illustrated in FIG. 4. 
Another type of prior art screwdriver is shown in FIGS. 6 and 7. This 
screwdriver has an end 11 which has a flat surface 13. Extending from the 
end 11 is a tapering section 15. Although slippage is reduced, this type 
may still damage the screw since it only contacts the screw at the bottom 
of the slot. 
In general terms the present invention is a tool for use with a fastening 
device having at least a first end with a predetermined configuration, 
such as the screw 18 in FIG. 2. The novel tool comprises a body 20 (see 
FIG. 3) which may consist of a shaft of any suitable cross-sectional 
configuration that may terminate in a handle (not shown). The present 
invention concerns the means 22 for engaging the predetermined 
configuration in the first end of the fastening device. The means 22 is 
attached to the body 20. In the FIG. 2 fastening device the predetermined 
configuration is a recess or slot 14, the first end is head 16 and the 
fastening device is screw 18. The means 22 for engaging of the novel tool 
has a first portion on surface 24 for contacting substantially the bottom 
of the slot 14. 
As is well known in the art, screws such as that shown in FIG. 2 have 
several standardized widths for the slot 14, the width depending upon the 
size of the screw 18. The surface 24, at a midpoint 23, as shown in FIGS. 
3 and 5, has a width substantially equal to the width of the slot 14. A 
connection segment 26 tapers and extends from the flat surface 24 and has 
a width less than the width of the flat surface 14 at a point 25 which is 
a predetermined distance from the flat surface 24. The tapering of the 
connecting segment 26 facilitates the engagement of the flat surface 24 
with the bottom of the slot 14. 
As shown in greater detail in FIGS. 8-11, a first end 30 is wider at its 
midpoint 32 than at either end 34, 36. The edge connecting the midpoint 32 
to the ends 34, 36 may be straight, as shown in FIG. 8 or smoothly curved 
as shown in FIG. 9. Due to the taper of section 38 which extends from the 
first end 30, an engagement area 40 is defined and is shown as the shaded 
triangular area in FIGS. 8 and 9. FIG. 10 depicts a side view of section 
38 also showing the engagement area 40. 
FIG. 11 illustrates in a top view engagement of the novel screwdriver with 
the slot 14 in the head 16 of a screw. The width of the first end 30 at 
the midpoint 32 substantially fits the width of the slot 14. As the 
screwdriver is turned, torque is applied to the sides of the slot 14 along 
the engagement area 40 of the section 38 as shown in FIG. 10. 
Surprisingly, the engagement does not begin at the midpoint 32, but rather 
a distance away from the midpoint 32 and increases towards the midpoint 32 
and up section 38 as the torque is increased. As a result a more positive 
engagement occurs between the slot 14 and the screwdriver. This result 
occurs for both embodiments shown in FIGS. 8 and 9. Preferably the 
midpoint is on each side of end 30 is 0.003 inches to 0.005 inches wider 
than the ends 34, 36. The overall size of the end 30 would be manufactured 
in different sizes as is well known in the art to fit different size 
standard screws. 
The invention is not limited to the particular details of the apparatus 
depicted and other modifications and applications are contemplated. 
Certain other changes, such as the configuration of the means for 
engaging, may be made in the above-described apparatus without departing 
from the true spirit and scope of the invention herein involved. It is 
intended, therefore, that the subject matter in the above depiction shall 
be interpreted as illustrative and not in a limiting sense.