The Fat Bead is a large diameter fiber-optic bead replacement sight. This sight features 2.6mm threads.
Specifications:

Type	Fiber Optic Bead
Frame Material	Steel
Frame Color	Black
Firearm Fit	Beretta, Benelli, Stoeger 2000/P-350 Pump
Base Configuration	2.6mm
Style
Front Material	Fiber Optic
Rear Material	N/A
Front Color	Green
Rear Color	N/A
Rail Size
Windage Adjustment
Elevation Adjustment
Fiber Diameter	.100"
Firearm Type	Shotgun