When your Mitutoyo BHN506 coordinate measuring machine stops behaving, two used replacement parts often show up at the same price: the Mitutoyo BHN506 Pressure Switch featuring a Sanwa Denki SPS-8T adjustable switch, and the Mitutoyo 908926 SRD Head 10/10. Both are Mitutoyo-branded components made in Japan and listed at USD 399.00 for the BHN506. Despite the shared price and machine compatibility, they are not interchangeable. One protects the machine from air-pressure problems; the other feeds position data back to the controller. Choosing the wrong one means your CMM stays down, so here's how to match the part to the fault.
Quick verdict
If your BHN506 is showing an air-pressure fault, losing air to the air bearings, or triggering an interlock, get the pressure switch assembly. If the machine moves but axis readings are erratic, repeatability is off, or the scale feedback is unreliable, the SRD head is the part you need.
Comparison
| Part | Job in the CMM | Listed Price | Price Bar |
|---|---|---|---|
| Mitutoyo BHN506 Pressure Switch (Sanwa Denki SPS-8T) | Monitors air pressure to air bearings and counterbalance system | USD 399.00 | |
| Mitutoyo 908926 SRD Head 10/10 | Reads linear scale graduations and sends axis position signals | USD 399.00 |
Where each product wins
Where the pressure switch wins. The Sanwa Denki SPS-8T pressure switch in the BHN506 assembly is your answer for anything related to pneumatic health. It monitors the air pressure that keeps the CMM's air bearings and counterbalance components working. When pressure dips below the safe threshold, it sends a fault signal to prevent damage to the guideways and axis mechanics. If your symptom is a pressure interlock or a machine that won't initialize, this is the direct replacement.
Where the SRD head wins. The 908926 SRD Head 10/10 is a reading head for the linear scale. It converts physical axis movement into high-resolution electronic signals for the CMM controller. If your machine moves but the position readout drifts, or if you're seeing scale errors during automated inspection, the SRD head is the component that restores clean feedback and repeatability. This is the part to focus on when the mechanics seem fine but the measurements don't repeat.
Product notes
Mitutoyo BHN506 Pressure Switch Sanwa Denki SPS-8T Coordinate Measuring Machine
This is the part to pick when your BHN506 fault is tied to air pressure. The assembly uses a Sanwa Denki SPS-8T adjustable pressure switch, and its job is to monitor the air feeding the ultra-sensitive air bearings and pneumatic counterbalance. If pressure drops, it triggers an interlock or fault signal so the machine doesn't run in an unsafe state. That makes it a safety-critical replacement for protecting the guideways and axis mechanics. One limitation: it won't resolve scale reading or position feedback problems. If your CMM is moving but coordinates are off, this switch isn't the fix. It's also a used component, so the used-part caveats apply. When your pressure alarm is active, this is the part to order.
Mitutoyo 908926 SRD Head 10/10 For Mitutoyo BHN506 Coordinate Measuring CNC
If your CMM is moving but position feedback is intermittent or measurements drift, the 908926 SRD Head 10/10 deserves attention. It reads linear scale graduations and translates axis movement into electronic signals for the BHN506 controller. Clean signals from this head are what keep positioning repeatability tight during automated 3D dimensional inspection. Because it's engineered specifically for the BHN506 CNC machine, it matches the system's scale and control architecture. The limitation: it does nothing for air-pressure or pneumatic faults. If your issue is a pressure interlock, this head won't fix it. And since it's a used part, examine the unit's condition before relying on it. For feedback and scale errors, this is the replacement that matches the symptom.
Final choice by use case
So the decision comes down to what your CMM is telling you. Order the Mitutoyo BHN506 Pressure Switch Sanwa Denki SPS-8T when your fault relates to air pressure, air bearings, or the pneumatic counterbalance. Order the Mitutoyo 908926 SRD Head 10/10 when your problem is axis feedback, scale reading, or repeatability. Both are used Mitutoyo parts for the same machine, but they fix different systems inside it. Match the part to the symptom and you'll get your CMM back to measuring.
