In order to get one of these to work you would have to grind the long walls along the inside of the tool so that it will fit around the 66-block terminal. I bought one of these ~6 months ago, sent Monoprice pics of it explaining the issue, including one of the bit stuck on the top 2mm of a terminal because it won't punch down all the way. They sent me a couple of replacements before I told them to stop wasting their money and just went and got my own somewhere else (for a lot more, perhaps, but it works!).
Until Monoprice comes out and says that they've gotten the manufacturer to change how they're making these so that they actually work, I truly recommend against buying this product.
PROS: There are no pros regarding the product itself - being inexpensive is only a pro if it works at all, otherwise it simply wastes your time. The only pro is that Monoprice is really great about returns.
CONS: It doesn't work - it will not fit around the 66-block terminal
I don't know what was going on with others finding this blade to small to fit. I tested it on a few different blocks from different manufactures that were produced over the last 20 years and it fit fine on all of them. I rate is an upper mid-level fully functional product. the finish is a little rough but honestly who cares. it works.
I hope I just got a defective blade. Maybe it did not get shaped properly. Great price. I could not find one cheaper than twenty dollars. I have to hold the 66 block and pull very hard to get the punch down tool off the pin.
PROS: it fits in my punch down tool and cuts the wire well.
CONS: It gets stuck on the pins of the 66 block. I have to hold the 66 block and pull very hard to get the punch down tool off the pin.
I discovered these bit problem comments after my defective bit arrived. This bit probelm has not been corrected. I pointed out that this is a known problem, but was blindly sent another useless bit. Insanity is doing the same thing over and over while expecting different results.
CONS: I have two of these bits, and both are too small to fit over the terminal. The replacement bit is even smaller than the original.
First, let me say that Monoprice's return system works very well, and quickly. I like Monoprice and have always got a good product at a good price. That being said, I bought one of these replacement blades to complete a home cabling job. It cracked on the second punchdown. When I received the replacement, it was way too tight to fit over the 66 terminal. I have the same blade for 110 terminals, and it works great. I think the tool is out of spec and that is why the first one cracked.
There are numerous reviews saying this blade won't fit a 66 block. Later followups seemed to indicate the issue was fixed. I took a chance and ordered one. They are still too small. I've already requested a RMA refund.