I am not to sure if it is my fault, or sigma not building to standards. I think it is my fault though.
My Sigma 1.4 tc which i use daily stripped the threads on the bolt that holds one side togeather.
I never gave it much thought. I use it on a fairly heavy lens and rarely let it hang from my neck. But on occasion I will let it drop if I am doing something that takes two hands.
The lens weighs about 6 lbs. So I am very careful now. The conection is fine and the camera connection is fine. But Sigma warrened me against it. They said they would try to increase the bolt size to help with heavy lenses. So I hope when i get it back it is fixed.
Just something to think about if you use heavy lenses. I never really gave it much thought. Until i was without a tc. I am mad at myself for this.