I got the 1.75" diameter diamond dry core saw with the SDS-Plus center bit. The center bit was not even close to centered when installed. I'm assuming the female threads were welded crooked on the end of the core bit. I made it work by pre-drilling the center hole (with a different bit) and then using a gloved hand to force the core bit to be close to center. Definitely not that safe. I removed the center after I had gone a few inches in. I only needed one hole through an 8" block wall, and it got the job done. If I was planning to use it a lot, I would have returned it to get one that was centered properly. They should have checked that before shipping it.