The little pieces that keep the loop fixed to the block are actually secured by small screws that on installation create the threads in the small loop holding piece. The problem is that there is always a side force on the block (and the loop) due to lateral movement and that makes the little screws break the thread that was created when they were inserted. As a result the small pieces that secure the loop to the block on both sides come out and the block inverts position. It happened to me, didn't take anything remotely close to 600kg for this to happen. The small pieces I am talking about have to made of metal! Also, one of these small pieces was already cracked on arrival (probably cracked during assembly) in one of the blocks I purchased. Overall, they are quite expensive if one considers the flawed choice of material for these small parts which affects the overall reliability of the product. Considering the long experience (and usual quality) of Antal products that I have on the boat I am quite disappointed with these Dynablocks and I don't recommend anyone to buy them until Antal revises the product. Don't understand how people can give 5 stars for this, yeah...looks great, fells great, therefore must be great...