The Turbo Snout and strainer are for a 3.5 in diam turbo. a filter goes between the T and L parts.
Suggest using heat resistant material on strainer and turbo snout.
The shape of the inside helps straighten air after passing through the filter.
The top twist locks onto the lower.
The hex mesh is just a strainer cap for a 3.5 in turbo. Using a screw tightened duct clamp around the outside is recommended for the hex mesh strainer.