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Description
Inside micrometer 25-50 mm – 0.01 mm resolution
Technical data and instrument construction
| Technical data | |
|---|---|
| Measuring range | 25-50 mm |
| Resolution | 0.01 mm |
| Micrometer screw pitch | 0.5 mm per revolution |
| Ratchet measuring force | 1-6 N |
| Measuring faces | cemented carbide, ground |
| Reading lock | locking screw |
| Included | adjustment wrench, 24.998 mm gauge |
READOUT0.01 mm
FACEScemented carbide
MEASURING FORCE1-6 N
GAUGE24.998 mm
MMWd caliper-type micrometer – construction and applications
Applications for an instrument with this measuring range
Inside micrometer 25-50 mm is an analog jaw-type instrument for measuring bore and bushing diameters and grooves with a readability of 0.01 mm. It works like a reversed outside micrometer: the jaws open inside the bore, and the result is read directly from the scale without conversion. The micrometer screw has a pitch of 0.5 mm, providing 50 divisions of 0.01 mm per thimble revolution.
The ground cemented carbide measuring faces retain their geometry over prolonged use. The ratchet limits the measuring force to 1-6 N, so the result does not depend on the operator's hand pressure, while the locking screw holds the indication during reading. The jaws reach approximately 10 mm into the bore — the instrument measures near the bore edge; a bore micrometer is used for deeper sections.
Typical applications:
- measuring bore and bushing diameters within the 25-50 mm range after reaming and boring,
- inspecting bearing seats and plain bearing bushings in machine housings,
- measuring the width of grooves and recesses between workpiece surfaces,
- in-process inspection at the machine tool and at the quality control station.
How to read the measurement
Sleeve and thimble scales step by step
Sleeve
37.50
+
Thimble
0.32
=
Measurement result
37.82 mm
The result consists of two readings. Whole and half millimeters are read on the sleeve — the whole-millimeter marks are above the reference line, and the 0.5 mm marks are below it. The sleeve numbering runs in the opposite direction to an outside micrometer because the dimension increases as the jaws expand. Hundredths of a millimeter are read on the thimble at the reference line. In the illustrated example, the thimble edge has passed the 37.5 mark, and the reference line indicates division 32, giving a result of 37.82 mm.
Steel expands by approximately 11.5 µm per meter for a temperature change of 1°C. A bore with a diameter of 50 mm that is 10°C warmer than the instrument is approximately 0.006 mm larger, or more than half a scale division. The workpiece and micrometer should be at the same temperature before measurement, preferably close to 20°C.
Find the maximum reading and do not force the ratchet
Measuring along a chord gives a reading that is too low — gently rock the instrument across the bore cross section; the correct diameter is the maximum reading in the plane perpendicular to the axis. Expand the jaws only with the ratchet until it starts to slip — excessive force distorts the result and accelerates wear of the measuring faces.
Set contents and zero setting
Preparing for the first measurement
INCLUDED:
| ✓ | adjusting wrench for sleeve adjustment during zero setting |
| ✓ | 24.998 mm gauge for checking the zero point |
Check the zero point using the supplied gauge: open the jaws inside the gauge using the ratchet and compare the reading with the 24.998 mm dimension marked on the standard. Correct any deviation by turning the sleeve with the adjustment wrench. Perform the check measurement at a temperature close to 20°C.
The 25-50 mm inside micrometer combines a simple, reliable analog design with 0.01 mm readability and constant ratchet force. The included gauge allows the zero point to be checked without additional equipment. It is an essential quality control tool wherever bore diameter measurement must be more reliable than with a caliper.
Frequently asked questions
A jaw-type instrument works like a reversed outside micrometer — the result is read directly from the scale without setting. A three-point bore micrometer centers itself in the bore and can be more accurate, but a single instrument covers a narrow range and requires a setting ring. A two-point bore micrometer must also be rocked in the bore to find the correct reading.
The gauge has a measured and marked actual dimension of 24.998 mm. Open the jaws inside it using the ratchet and compare the reading with this value — correct any difference by turning the sleeve with the adjustment wrench. Check the zero point at a temperature close to 20°C and repeat the check whenever the instrument is dropped or overloaded.
The internal dimension increases as the jaws open, and the thimble rotates in the opposite direction to that used for external measurement. The thimble edge therefore covers successive marks with progressively smaller values. The reading principle remains the same: millimeters from the sleeve plus hundredths of a millimeter from the thimble.
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Shipping
All orders are delivered by courier company GLS. For orders exceeding 369 PLN gross shipping is FREE
| Courier GLS | Przelew24 / Prepayment | 14,76 zł gross | Delivery time 1 working day |
| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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