If your shop runs a Mitutoyo BHN506 coordinate measuring machine, the quiet hero of every accurate measurement is the reference sphere you use to qualify the probe. A probe that hasn't been calibrated against a master ball can introduce errors into every dimension you report. The Mitutoyo 06AAC557 Master Ball is designed to be that point of truth for this specific CMM, and this listing offers one at USD 1,299.00.
Quick verdict
This is a Mitutoyo 06AAC557 master ball, sold in used condition, built for the BHN506 coordinate measuring machine. It is a high-precision calibration standard meant to support probing system alignment, tip qualification, and error compensation. If you have a BHN506 and need a dedicated reference sphere from the same maker, this is the exact part to look for.
Who it suits
The 06AAC557 makes sense for dimensional metrology machine inspection work where a BHN506 is the primary CMM. Quality labs, machine shops with in-house inspection, and calibration teams that need a repeatable reference for probe qualification will all find this sphere purposeful. If the BHN506 is not the machine on your floor, then this part does not match your need, and it is better to source a master ball built for your specific CMM model.
What stands out from the listed details
The model number, MPN BHN506, and the description all point to one application: the Mitutoyo BHN506 CMM. The part is made to act as a master qualification sphere, with high-precision sphericity and wear-resistant materials. For a measurement system that lives on repeatability, having a dedicated reference sphere that is identified for the machine removes guesswork from the calibration process. The country of origin listed is Japan, which will matter to shops that prefer a Japanese-sourced Mitutoyo part. This is sold as parts for a coordinate measuring machine, so it belongs in the CMM tooling category rather than in general shop accessories.
Meaningful trade-offs
The biggest trade-off is condition. At USD 1,299.00, you are paying a significant price for a used calibration standard. Since the entire point of the master ball is to be the stable reference for your probe, the prior handling of this sphere matters. A used reference carries more uncertainty than a new one, and you are trusting the previous owner's care. Also, because the ball is specifically tied to the BHN506, it is not a universal CMM accessory. This is a one-machine decision, which is fine if the BHN506 is yours and a problem if it is not.
Bottom line
The Mitutoyo 06AAC557 master ball is the right reference solution when your CMM is a Mitutoyo BHN506. The used condition at $1,299 is the main point to weigh, but for a shop that already depends on this machine for inspection, having the correct master qualification sphere from Mitutoyo is a practical step toward trustworthy measurement results.
