What's in the box:

ZTTO MTB Bicycle Single Speed Derailleur Bicycle Chain Tensioner For Hanger Dropout Frame Adjustable Bike Pulley Wheel (Standard)

Features:
Onverts any multi-speed bike to a single speed.
Spring loaded design accommodates a wide range of cog sizes.
Extremely lightweight.
Adjusts for perfect chain tension.
Adjustable chain line.Applicable for: outdoor bicycles, mountain bikes and etc
Prevents chain from falling off, reduce tooth feeling

Specifications:
Material: Aluminum alloy
Application: single speed folding bicycle
Color: black and red
Item weight: 59g / 2.1ounce
Package size: 150 * 80 * 60mm / 5.9 * 3.1 * 2.4in
Package weight: 63g / 2.2ounce

Packing List:
1 * Bicycle Single Speed Derailleur