Key Features:

Capacity: ‎0.25 Inches 
Material: Steel
Item Diameter: 0.25 Inches
Compatible Devices: Lathe
Thread Size: 1/4-20 UNC

Shank Diameter: 1/4"

Accept Shank Size: 1/8" and 1/4" Shank

Extend Length: 2-1/8”

Wrench Spanner: ER16 M Type

Please check product compatibility carefully to ensure it is the product you need.
So as not to waste your time and energy on return.

Details:
This router collet extension chuck accepts both 1/8" and 1/4" shank router bit for converting and extending.
Converter Adapter and ER16 Spring Collet Made of steel for maximum strength and long life use; ER16 M Type Collet Chuck Wrench Spanner Made of High Carbon Steel, Anti-slip handle Design, for ER16 M Lathe Clamping Nut.
High precision, stable performance. Extend your router bit to provide the full depth of cut, for both 1/8 inch and 1/4 inch shank router bit.
Eliminate the dangerous temptation of withdrawing the shank from the collet, extend the bit to provide the full depth of cut. Place the router collet extension shank in the 1/4-inch router collet and the router bit shank in the extension collet and tighten both.
This router collet chuck provide the additional depth of cut needed for many routing tasks. Easy to use, better to control, it will improve your work efficiency. 

Package Including:

1PC 1/4" shank collet extension

1PC ER16 1/4" Collet

1PC ER16 1/8" Collet

1PC ER16 M Type Collet Chuck Wrench Spanner

as the picture