Was a tight fit but workedI ordered this item for my pentair 160317 unit - This is the part that the manufacturer and the site from amazon recommended. I saw may disgrunted responses on the installation efforts and size issues.I will confirm that this is the correct size. There are many who disagree. However if you receive the correct part number 87200400 this is the correct item to install.I was able to figure out how to install this by used an earlier response and my "estimation" on what to do to correctly install.If you use a 3 inch clamp setup (DO NOT DO THIS IF YOU ARE NOT FAMILIAR WITH CLAMPS - It can result in injury).1) Do not remove anything after taking the top off.2) Clean all passages and areas of former use. Get rid of all prior silicone lube, grease and accumulated dirt (This took almost one hour)!3) Have the O-Ring in sun for at least 30 minutes.4) Clean top where connection was made prior by using bleach or heavy duty cleaner.5) You should have a clean setup for moving forward.6) Install 3 vise grips (3 inched each) Two midway (See my photo) and one between the two (Photo)Easy to install.Fits perfectly for my pool water filterFit old pentair filter reservoir , really tight fit requires lubricant. now it is somewhat difficult in a good way, to remove the dome from the reservoir. this helps the pump system flow at optimal power and keeps the pool clean more efficiently. these minor details do affect the effectiveness of the pump and motor. remember less of a seal= more air in the system.Actual Pentair o-ring that fits well and shipped quickly but shipping cost seems high.I bought this to replace the leaking oring on our Pentair Clean and Clear 100 filter. I left the oring in the Las Vegas sun for 10 minutes before installation and it stretched out easily around the housing. I cleaned and applied lube on the inside of the top lid and the oring and it slid into place with a snug fit. So far no leaks after 12 filter cycles. From looking at the other reviews, it seems that most of the problems with the oring are installation errors of not enough lube being used causing the oring to either be cut or pinched and not warming up the oring enough to allow easier stretching.WE COULDN'T BELIEVE THE AMOUNT OF LINT THAT THIS TOOL REMOVED. WE USED THE BRUSH TO LOOSEN ANY OLD DRIED LINT AND THEN SUCTIONED OUT THE VENT FROM THE DRYER END. THEN WE WENT OUTSIDE AND DID THE SAME FROM THE OUTSIDE VENT. WHEN WE WERE FINISHED AND NO MORE LINT CAME OUT THE VACUUM CUP WAS ALMOST FULL. WE NOTICED IMMEDIATELY HOW MUCH BETTER THE DRYER FUNCTIONED. THIS TOOL WILL GIVE YOU PEACE OF MIND AND PRESERVE YOUR DRYER.Works well.Yes very satisfiedThank you!