A metric chrome bar can serve an inch design when the inch dimension is treated as a functional requirement and converted to a metric diameter with a metric tolerance band. Metric bar is supplied in millimeters. The drawing may stay in inches, but the order, the drawing note and the inspection record should be in millimeters and micrometers so the fit can be recalculated before the bars are cut.
Can I use a metric chrome bar on an inch drawing?
Yes, in most cases, as long as the inch size is a functional requirement and not a fixed purchase size.
Most inch designs do not depend on the shaft being exactly 1.000 in. They depend on the clearance or interference the shaft makes with a bore, a seal, a bearing or a bushing. Where that is true, the workable path is to convert the inch nominal to millimeters, choose the metric diameter that reproduces the intended fit, and state that diameter with its tolerance band on the inquiry and on the drawing. The inch drawing continues to govern what the part has to do; only the way the diameter is specified changes.
Where the mating component is inch-sized and cannot be changed, the metric diameter and its tolerance band have to be checked against that bore before the order is placed, because the difference between an inch nominal and the nearest metric size has to be absorbed by the fit.
Yixin Precision Machinery (Changzhou), whose brand and domain is YXROD, supplies metric sizes only. The 45 Steel Chrome-Plated Soft Shaft and the 45 Steel Ground Round Bar, for example, have a standard range of Ø4–140 mm, with diameters up to Ø200 mm made to order. There is no inch-size stock, and no inch nominal is quoted as a catalogue size. Sizes are stated in millimeters throughout the quotation, the packing list and the mill certificate.
Which metric diameter fits an inch bore?
Choose the metric diameter that reproduces the fit, not the one that comes closest to the converted nominal.
A 1 in bore is 25.4 mm. A Ø25 mm bar is 0.4 mm smaller at nominal, so the clearance is set by the bore tolerance and the shaft tolerance band together, not by the nominal figure alone. This is why the inquiry should carry the bore diameter and its tolerance in millimeters, alongside the shaft diameter you are considering.
Yixin standard diameter bands are −0.02/−0.05 mm for Ø4 mm to Ø11 mm. From Ø12 mm the band is selected per order from 0/−0.02 mm, −0.01/−0.03 mm or −0.02/−0.05 mm. The expected fit range is the bore tolerance plus the shaft tolerance. If the result does not match the intent of the drawing, move to the next metric diameter rather than assume the converted one will work.
Two conditions apply at the smaller end of the range. Quenched and tempered bars start at Ø8 mm, so Ø8 mm to Ø11 mm follows the small-diameter band, while the 40Cr Q&T Ground Round Bar starts at Ø5 mm. Where a seal or a linear bearing is part of the assembly, check its bore range against the chosen metric diameter and band before the order is placed.
How do I convert inch tolerances and chrome thickness to metric?
Multiply the inch value by 25.4 for millimeters, or by 25 400 for micrometers, then compare the result with the metric band offered for that diameter.
| Inch value on the drawing | Metric equivalent | What it is used for |
|---|---|---|
| 1.000 in nominal | 25.4 mm | converted to a metric diameter and a tolerance band |
| 0.001 in | 0.0254 mm, or 25.4 μm | diameter tolerance; compare with the band offered |
| 0.0005 in | 12.7 μm | fine diameter or finish calls |
| 16 μin Ra | ≈0.41 μm | surface finish call; compare with the stated finish |
Chrome thickness is quoted per side, not as a change in diameter, so a diameter check has to allow for the layer on both sides of the bar. Yixin hard chrome runs from 10 μm to 50 μm per side, chosen per order, which is about 0.0004 in to 0.002 in per side, and the chrome hardness is stated as HV800+. Surface finish is stated as Ra ≤ 0.4 μm on chrome surfaces and Ra ≤ 0.8 μm on ground surfaces, so a 16 μin Ra callout at 0.41 μm sits just above the stated chrome finish. Straightness is approximately 0.1 mm/m from Ø25 mm and approximately 0.2 mm/m below that diameter.
Which grade and hardness should an inch-designed shaft use?
Match the grade and the condition to the load and to the machining, not to the inch nominal.
| Yixin product | Base and condition | Hardness as stated | Size range |
|---|---|---|---|
| 45 Steel Chrome-Plated Soft Shaft | 45 steel, not induction hardened, then hard chrome | base about HRC17 | Standard range Ø4–140 mm; up to Ø200 mm made to order |
| 45 Steel Induction-Hardened Chrome Shaft | 45 steel, induction hardened to a case about 2 mm deep, then hard chrome | case ≥ HRC55 | Ø4–130 mm |
| 45 Steel Chrome-Plated Linear Shaft | same route as the induction-hardened chrome shaft | case ≥ HRC55; 0/−0.02 mm typical for linear bearings | Ø4–130 mm |
| 45 Steel Q&T Chrome-Plated Bar | Q&T base, then hard chrome | surface HRC25–28 or HRC28–32, chosen per order | Ø8–140 mm |
| 40Cr Q&T Chrome-Plated Bar | 40Cr Q&T core, then hard chrome, made to order | HRC28–35 | Ø8–140 mm |
| 42CrMo Q&T Chrome-Plated Bar | 42CrMo Q&T, then hard chrome, made to order | HRC30–38 | Ø8–100 mm |
The 45 Steel Chrome-Plated Soft Shaft suits mechanical support and guidance, general sliding fits, and light-duty rods whose ends need substantial machining; it is not for rods that need an induction-hardened case. For a harder wear surface, choose the 45 Steel Induction-Hardened Chrome Shaft. The Q&T chrome-plated bars are quenched and tempered, not surface hardened, and have no induction-hardened case; on the 45 steel Q&T bar the stated HRC25–28 or HRC28–32 is a surface value and the core is softer, because grade 45 has limited hardenability. The 40Cr Q&T bar is HRC28–35, and 42CrMo Q&T at HRC30–38 is intended for heavy or shock loads.
Grade names lead with the GB grade and standard: Grade 45 to GB/T 699-2015, and 40Cr and 42CrMo to GB/T 3077-2015. C45, S45C and SAE 1045 are comparable to Grade 45 for reference only, as are 41Cr4 and SCr440 for 40Cr, and 42CrMo4 and SCM440 for 42CrMo. Chemistry limits differ between standards, so the GB grade governs the order.
How do I inspect and order a metric bar against an inch drawing?
Convert the drawing limits to millimeters once, put the metric values on the order, and inspect in metric units.
Diameter is measured in millimeters against the band on the drawing. Chrome thickness is checked per side against the layer ordered, within 10 μm to 50 μm. Chrome hardness is stated as HV800+, and finish is checked against Ra ≤ 0.4 μm on chrome and Ra ≤ 0.8 μm on ground surfaces. Straightness is approximately 0.1 mm/m from Ø25 mm and approximately 0.2 mm/m below that diameter. Full bars come in 4 m, 6 m, 7.5 m or 8.1 m lengths, and bars are CNC cut to length from 200 mm, with ends left as sawn by default, so an inch cut length is converted to a metric cut length. Threading, chamfering or center holes can be specified on the drawing and are machined by partner plants to Yixin's specification before delivery. Per-order third-party inspection is arranged on request.
The route behind the surface matters when the shaft is going into a cylinder or a linear axis. On the 45 Steel Chrome-Plated Soft Shaft the sequence runs from cold drawing or peeling through roll straightening, centerless grinding and polishing to hard chrome and final polishing. Hard chrome plating and machining are done by long-term partner plants to Yixin's specification, and chrome thickness, diameter and surface are checked before packing.
What to put in your RFQ
- The function of the shaft: hydraulic cylinder rod, linear bearing shaft, guide pin, or a sliding fit in a bore or bushing.
- The mating bore diameter and its tolerance in millimeters, plus the metric shaft diameter and tolerance band you want. If the original drawing is in inches, give the converted metric values rather than the inch nominal.
- Grade and condition: 45 steel, 40Cr or 42CrMo, and whether the surface has to be induction hardened. State that Q&T bars are quenched and tempered and carry no induction-hardened case where that matters.
- Surface: ground only or hard chrome, with the chrome thickness in micrometers per side if a specific layer is required.
- Cut length in millimeters, quantity in pieces or kilograms, and whether sawn ends are acceptable. Export orders start at 1 t; samples of 20–50 kg are charged, with the sample fee refunded on a formal order and freight paid by the buyer.
- Finish and straightness callouts in metric units, and any third-party inspection to be arranged on request.
- Delivery and packing: FOB Shanghai or Ningbo, T/T only, with a 50% deposit and the balance before shipment, and for export bars wrapped in bubble film and packed in wooden cases, with no steel straps on finished bars.
Send diameters, lengths, quantities or a drawing. Quotation reply within one working day, with grade, tolerance, chrome thickness and lead time.
Summary
A metric chrome bar works in an inch design when the inch dimension is treated as a functional requirement. Convert the inch nominal to millimeters, choose the metric diameter that reproduces the intended fit against the actual bore, and state that diameter with a metric tolerance band. Convert tolerances at 25.4 mm per inch, quote chrome thickness per side in micrometers, and inspect in metric units. Match the grade and condition to the load, name the GB grade first, and treat foreign grades as comparable references only.
References
- GB/T 699-2015, Quality carbon structure steels — the standard against which Grade 45 is stated.
- GB/T 3077-2015, Alloy structure steels — the standard against which 40Cr and 42CrMo are stated.