If it's the same as a 2003 1500 series (which I'm sure it is) it should be a T-55 torx bit.
This is what it is...
it is a T-55
T-55
You will need a T55 Torx bit to remove the front caliper of a 2001 Silverado 1500. A torx bit is a screw with a six point star shaped head. These come in different sizes.
Torx is a 50 and they are really tight.
T - 55 TORX, Across the board for similar GM's.
55
44
T55
Torx #47
T60. It's a torx bit.
The 2004 Silverado HD uses a t-55 torx bit to remove the caliper. The torx can be found and most any auto parts.
T-55