Pete:

Although an allen wrench may work, it is not recommended by mechanics like me. If it does not work, you take a chance of rounding the shoulders on the screw head. Likewise, phillips head, spline drive, or star drive (These are rare, but do exist here in the USA.) should not be used on torx head screws.

Of course, if you are out in the "boonies" and you have to improvise, give it your best shot.

Bountyhunter