At441 Hss Microstop Countersink

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Part# 12-01591
MFR Model# 02-441


AT441 HS Micro Stop Countersink, similar to the AT442SLS unit, except with 1/4-28 female threaded nose to accommodate AT455 cutter.

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WARNING: Cancer and Reproductive Harm -


Kerry H Verified Purchase


December 6, 2023

Don’t waste your time and money on this micro stop. It has a reverse-thread lock nut that jams when you lock it down (by hand) and it will not come loose for resetting even with channel locks and a vice. Don’t know why it does this, but it happens whenever you set the lock nut. Spend the extra money and get the better one.

Reginald C Verified Purchase


September 16, 2023

Do not use stop nut. Gently unscrew/retract nut out of the way (not really needed) as it could jam. After I did this it worked flawlessly. An amazing tool which set countersink depth easily and consistently. Very nice!

Daryl B Verified Purchase


August 23, 2023

James G Verified Purchase


January 12, 2022

The tools are working as advertised.

Sergio D
August 21, 2020

The first one of these I received immediately seized up at the point at which the lock ring meets the drill side of the cage barrel. I was unable to loosen it, to the point where I fractured the cage with the force of a bar passed through the cage openings. Aircraft Spruce promptly replaced the unit without additional charge, which was great customer service. I applied anti-seize compound to the threads on this second unit. That seems to have solved the problem so far. The unit does a nice job of cutting multiple countersinks to the same depth, but the manufacturer really ought, in my opinion, provide an instruction sheet on how to use and adjust it.

James C
January 13, 2023

The first one of these I purchased somehow managed to get cross threaded the first time I used it. After a few uses it became so distorted a pneumatic impact wrench couldn’t loosen the collet. I have now purchased a second only because there aren’t many affordable options that ship in timely fashion available. TBD how long it will last.

Lucas A Verified Purchase


February 15, 2022


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Q: what type of base does this have? Is it nylon or have needle bearings?

This has a plastic base and bronze bearings.

Q: What size is the O.D. of the cage itself?

Approx 7/8 to 1 per the vendor.

Q: 1- How is the countersink mounted, thread or set screw? 2 - If thread what size threads? 3 - Is a 120 Deg countersink or a 100 Deg countersink supplied? 4 - Can I get a 120 Deg countersink instead of a 100 Deg countersink with the unit if so supplied? Thank you, Barry

The counter sink threads in using 1/4-20 threads. The only 120 deg countersinks we offer come in a 5 piece set under part number 12-02884. The countersink cutters much be purchased separate from this countersink stop.