The In-Line Spark Arrestor is a metal box with collars at each end that goes onto your stove prior to your first piece of stove pipe.  It has a metal screen that can slide in and out which catches sparks before they enter your stove pipe. 

The In-line Spark Box is designed to have a spark arrestor just above the stove.

Currently the 4" & 6" versions are silver model seen in last picture.

Prevents almost all ash and sparks from going up a stove pipe and onto wall tent roof.

You can clean your inline spark arrestor daily, in 15 -20 seconds, without having to take down all of your stove pipe to clean the spark arrestor that is on top of your pipe.

Known as an In-Line Spark Arrestor, In-Line Spark Box, and Stack Robber.