Update- after ordering, recieving several different jack lugs & being able to use these in pairs- I need to update this review -The build on this product is comparatively very beefy to many jack lugs on the market. The back, top& angle plates are the thickest gauge metal out of 4 Jack lugs I now have and use. In fact this is overall the nicest Jack lug I currently have and use- ecept for the diameter of the spindle. Despite my DESIRE to have larger spindles across ALL the lugs I use - This doesn't effect its use and has not caused any deformation or failure problems! It just doesnt fit snug like my lifting lacks do. They DO however LIFT WITHOUT FAILURE! I use this product with another lug on the opposite side of container always to prevent sliding. This lug has actually become one I use often along with another black one that has a similar build ( slightly bigger spindle). Being able to compare many of these side by side and TOGETHER really changed my perspective and expectations overall. Finally the math made me feel alot better as well. ( ie fully loaded 40ft weighs ~ 67k divide by 4 and you get ~17k. I figure even on loaded containers corner jack lug is lifting 17-34k or 9-12 tons max. So you will never really be putting 74k or more on one of these jack lugs anyway!This IS safe to use ! Easily in the top 2 out of 4 I have ! Giving this another star to reflect how it compares to others !Previously-Wanted to love it really. Ive wanted some of these for a very long time. Overall , it's built pretty tough & the shape of the bottom edge is perfect for clearing the ground , twisting the jack lug into position- this is a pretty neat design detail. The handle is convenient for carrying and for holding it in place while jack positioned , BUT WAIT ...The diameter of the lifting rod? or lifting spindle? , not sure what to call it but is quite a bit smaller than my other container lifting jacks. AND WHY am i having to hold this thing here while i getki my jack into place????? Maybe This is OK FOR EMPTY CONTAINERS. To be fair the lifting jack units I'm comparing this to are rated for lifting fully Loaded containers from a truck bed and lowering to the ground or picking up loaded containers so a flatbed can roll in underneath. See the pictures for the comparison. The main difference you'll notice is the lifting jack sports a MUCH larger diameter spindle to fit into the corner blocks with ZERO PLAY. Now this spindle on the bigger jack is hollow as far as i can tell BUT...I believe the size of the spindle matters...lol...it creates a solid connection and changes the physics at play. With this larger spindle we are using the corner block as it was designed to be used. WITH A FIT LIKE THIS YOU DONT NEED TO HOLD ANYTHING STILL WHILE PREPARE PART B it just stays put. With a bigger well fitting spindle- the weight is spread evenly over the top curve which is in full contact with the block ..there is no room to shift or bend downward as the spindle is snug in the block from the underside as well ( IT can NOT bend downward as it's supported by The block keyhole ITSELF the only way to bend downward would be to bend the corner block itself - and that's NOT HAPPENING) SO The pressure exerted on the top of the spindle while lifting is supported by the snug fit which prevents any bending & ensures the pressure is transfered back to the lower section of the spindle and the corner block. The weight on THIS bottle jack lug is really Very concentrated over a much smaller area and since there is NOT a snug fit bending force due to the fulcrum point pressure created is completely possible. I am actually a bit hesitant to use this on my container as it is NOT empty. This Jack Lug would likely be ok with an empty container & if you only need to make small adjustments in leveling. BUT then what if you need to adjust it later when it IS full.. ?? I can not recommend it's use for raising 4inchs or more at all and I feel honestly anything more than 2inch requires 2nd jack lug on the opposite side (same end) so that the entire end is being lifted together. The play in the keyhole allows too much chance for bending, shifting, and odd folcrums which if your already on concrete on other corners can lead to slipping and sliding. Do I recommend this Jack Lug? Ugh in its current state I feel if you have 2 of them and you container is empty you could probably safely lift one end and get some blocks or boards under it but the other draw back to these types of jack lugs is also that the jack is where you need to put in leveling blocks etc. This is an issue with any corner lift device for containers though. I am pretty certain I can not lift my container with this device. If I decide to give it a go I will record the effort. I feel these need to be used in pairs 100% though as do most Jack's and lifts for containers and since I only recieved the one for reviewing, I can only speculate about the lifting aspects of it. My container is curently 1ft off the ground - I have lifted this container alot of different ways in the decades I've owned it - devices similar to this have always been something I've wanted to use. There are versions of these that probably have snug fit. This particular device sets the jack out towards the end of the lift surface a nice heavy ring retains the bottle jack aiding in its retention. When beimg lifted it exerts pressure toward the container .. this should help the bending spindle issue but also pushes on the container a bit so with out an opposing force opposite I'm not comfortable testing it 1ft off the ground. I will try to set up further experimentation with this unit on a friends container and come back with more insight. For now I'm giving this 3 stars - I believe for empty container adjustments its good to go. BUT with a properly sized spindle I'm pretty sure this would lift a container in any state of loading and be a tool that remains useful past loading date. It seems a waste to cut this corner & not take advantage & the corner blocks properly so it's value is limited to any windo of time a container might be empty. For myself , I try to buy tools that will work with me as I progress further into a project. This doesn't feel like it makes the cut on this level.