One Case Size, Two Metric Codes: the 1225 Problem

We parsed all 234,815 rows of Walsin’s chip resistor export. The 1225 chip resistor size is written 1225(3264) on 1,708 rows and 1225(3263) on 47. 1225 imperial is 3.2 × 6.4 mm, so 3264 is right and 47 real parts carry a wrong metric code.

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A case-size string is the one field everybody filters on and nobody checks. Filter on 1225(3264) and you get 1,708 rows, a clean-looking result and no warning. The 47 rows you did not get are the only metal foil parts at that footprint, and they are the only ones at 1225 that reach ≦±50 ppm/°C.

Venatech Limited, an authorised Walsin distributor in Hong Kong, holds all 203 of Walsin Technology (Walsin) parametric export files. This post is measured from the 137 chip resistor files, of which 64 return rows, and specifically from Thick_Film_Wide_Terminal_Power_Chip_Resistor__1of1.xlsx and Metal_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx. Every part number below is real and every count is of part numbers, not pieces.

How is the 1225 chip resistor size written in Walsin’s export?

Two ways, in two different files. We re-counted both: the Size column reads 1225(3264) on 1,708 rows and 1225(3263) on 47, for 1,755 rows at the footprint in total. The split is perfectly clean along product lines. Every one of the 1,708 is in the Thick Film Wide Terminal Power Chip-Resistor group. Every one of the 47 is in the Metal Foil Low Ohm Power Sensing Chip-Resistor series. No file mixes the two spellings.

Size string	Rows	Series group	File	Match / mismatch vs 3.2 × 6.4 mm
1225(3264)	1,708	Thick Film Wide Terminal Power Chip-Resistor	Thick_Film_Wide_Terminal_Power_Chip_Resistor__1of1.xlsx	Match — 32 and 64 tenths of a millimetre
1225(3263)	47	Metal Low Ohm Current Sense Chip-Resistor	Metal_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx	Mismatch — 63 implies 6.3 mm, not 6.4 mm

We have not seen this counted anywhere. It is a two-character defect in one column of one file, it affects 47 part numbers, and it is invisible to every reader who trusts the field.

Which metric code is arithmetically correct for 1225?

3264. The imperial code 1225 means 0.12 by 0.25 inches. 0.12 inch is 3.048 mm and 0.25 inch is 6.35 mm, which round to 3.2 × 6.4 mm, and the metric EIA code is simply those two figures in tenths of a millimetre: 32 then 64. So 1225(3264) is internally consistent and 1225(3263) is not — 63 would be 6.3 mm, which is not what 0.25 inch rounds to and is not a standard code anywhere else in the export.

Every other imperial code in the file follows the same arithmetic and does so once. We checked all of them: 0201(0603), 0402(1005), 0603(1608), 0805(2012), 1206(3216), 1210(3225), 1218(3248), 2010(5025), 2512(6432), 0612(1632), 1020(2550), 0306(0816), 0815(2037) and 01005(0402). Fourteen codes, fourteen one-to-one mappings. The 47 rows are the only arithmetic failure in 234,815.

What exactly do the 47 mislabelled rows contain?

Walsin’s entire metal foil power sensing shelf at 1225. We read all 47: resistance from 0.0005 Ω to 0.025 Ω, rated power 2 W on every row, tolerance ±1% on 26 rows and ±0.5% on 21, and TCR ≦±50 ppm/°C on 42 rows with ≦±100 on the remaining 5. WW25YR0L5FTL is the 0.0005 Ω part, WW25YR001FTL is 0.001 Ω and WW25YR010FTL is 0.010 Ω.

That is a sub-milliohm current-sensing range in a 2 W wide footprint, not a duplicate of something else. It is also the tightest TCR grade at 1225: the 1,708 rows under the correct code offer ≦±100 ppm/°C at best, on 738 rows, and ≦±200 on 922. Every single part at 1225 that reaches ≦±50 ppm/°C carries the wrong metric code.

What does a filter on 1225(3264) silently drop?

The whole range below 0.1 Ω. We compared the two resistance distributions and found zero overlapping values. The 47 rows span 0.0005 Ω to 0.025 Ω. The 1,708 rows span 0.1 Ω to 1 MΩ. Nothing in the export sits at 1225 between 0.025 Ω and 0.1 Ω, so the two metric codes do not label two versions of the same shelf — they partition the footprint into two disjoint resistance ranges, and a filter on the correct code returns only the upper one.

The consequence is a specific wrong conclusion, not a missing row. An engineer who filters 1225(3264), sees 0.1 Ω as the lowest resistance and concludes Walsin builds no milliohm shunt in a wide 1225 footprint has been misled by two characters. A 2.7% data loss is easy to shrug at; losing the whole sub-0.1 Ω range and the whole ≦±50 ppm/°C grade at that footprint is not.

Is 1225 the only case size in the export with two metric codes?

Yes. We parsed every distinct Size string in the chip resistor export — there are 19 — and split each into its imperial part and its parenthesised metric part. Fourteen imperial codes map to exactly one metric code each. 1225 is the only one that maps to two. Three more strings carry no metric code at all because they are array formats written with a multiplier: 0602*8 on 555 rows, 0201*4 on 194 and 0201*2 on 194, which is 943 rows with no metric code to compare.

So this is not a general looseness in the data. It is one defect in one series, which is the kind that survives longest, because nobody builds a validation rule for a column that is right 99.98% of the time. We have published before that the MLCC export carries no metric code on any of its 24,026 rows while all 234,815 chip resistor rows do; this is the same field failing in the opposite direction.

How do the two 1225 populations compare part by part?

They share a footprint, a 2 W rating and nothing else that matters. We put one row from each shelf side by side against a 0.010 Ω, ≦±50 ppm/°C, 2 W requirement in a wide terminal 1225. Only one shelf can serve it, and it is the one the filter drops. We will not tell you a part is equivalent. We will show you where it differs.

Part number	Series	Size as written	Resistance	Tolerance	TCR	Rated power	Match / mismatch vs 0.010 Ω ≦±50 ppm/°C 2 W at 1225
WW25YR010FTL	Metal Foil Low Ohm Power Sensing	1225(3263)	0.010 Ω	±1%	≦±50	2 W	Match on all four — and mismatch on the metric code, which is why you will not find it
WW25YR0L5FTL	Metal Foil Low Ohm Power Sensing	1225(3263)	0.0005 Ω	±1%	≦±100	2 W	Match on size and power; mismatch — 20× lower resistance, 2× the TCR
WW25YR005FTL	Metal Foil Low Ohm Power Sensing	1225(3263)	0.005 Ω	±1%	≦±50	2 W	Match on TCR, power and size; mismatch — half the resistance
WW25LR100FTL	Thick Film Wide Terminal Power Low Ohm	1225(3264)	0.100 Ω	±1%	0 ~ 350	2 W	Match on size and power; mismatch — 10× the resistance, one-sided TCR notation
WW25L0R10JTL	Thick Film Wide Terminal Power Low Ohm	1225(3264)	0.100 Ω	±5%	0 ~ 350	2 W	Mismatch — ±5% tolerance and a TCR stated as a one-sided band
WK25L1R00FTL	Thick Film Wide Terminal Power	1225(3264)	1.00 Ω	±1%	≦±200	2 W	Mismatch — 100× the resistance, 4× the TCR
WK25L1R10FTL	Thick Film Wide Terminal Power	1225(3264)	1.10 Ω	±1%	≦±200	2 W	Mismatch — the nearest value on the correctly coded shelf is 100× too high

Confirm against both datasheets and qualify in your own circuit — that step stays with you. Note the notation difference too: 48 of the 1,708 correctly coded rows state TCR as 0 ~ 200 or 0 ~ 350, a one-sided band that will not range-filter numerically, while all 47 mislabelled rows use the symmetric ≦± form.

Do we hold a datasheet that settles which code is right?

No, and that is why we are arguing it from arithmetic. We hold 28 Walsin datasheets, 451 pages, and exactly two are chip resistor sheets: Walsin_MR_Automotive_Thick_Film_Chip_Resistor.pdf and Walsin_WR_General_Purpose_Chip_Resistor.pdf. Neither covers the WK wide terminal series or the WW metal foil series, so we cannot read a dimensional drawing and confirm the body length to a tenth of a millimetre.

What we can do is state the inference and its limits. 0.25 inch is 6.35 mm, the metric code is dimensions in tenths of a millimetre, every other code follows that rule, and 6.3 appears nowhere else in 234,815 rows. That is a strong case for a transcription error rather than a genuinely shorter part — but it is an inference, not a measurement of a part.

Where we can be checked, we are. UL file E182369 covers Walsin’s safety capacitor line and is searchable in UL’s own public database in about thirty seconds. Ask for the datasheet covering your part number and it arrives in your inbox rather than in a brochure. We will tell you what we do not have. Most distributors will not.

What should a buyer in the United States or Germany do about it?

Search the imperial code as a substring, never the full string. Searching 1225 returns all 1,755 rows; searching 1225(3264) returns 1,708 and tells you nothing is missing. We checked the dated snapshot as at 23 September 2026 too: of its 1,125 catalogue codes, 254 are chip resistors and three are WW low-ohm parts, all at 0805, so a 1225 metal foil part is an order-in line today. The trade press reported passive component lead times stretching through 2026 as AI server and electric vehicle programmes pulled on the same capacity.

1. Match on the imperial code and verify the metric one. Treat the parenthesised code as a field that can be wrong, because in 47 of 1,755 rows at this footprint it is.
2. Cross the whole BOM in one pass. Paste up to 500 part numbers or drop your Excel or CSV into the free cross-reference tool. It is matched against Walsin’s published catalogue and returns candidates field by field, with every difference from your original stated rather than hidden.
3. Check what is physically in Hong Kong on ready stock before you commit to a production slot. It is a dated snapshot as at 23 September 2026, not a live feed.

For the three wide terminal footprints and what each one buys, see wide terminal power resistors: 1225, 1020 and 0612. For the imperial-and-metric mapping across the whole catalogue, see passive component case sizes, imperial and metric. For the shelf these 47 parts belong to, see low ohm current sense: thick film vs metal. The full range is on the Walsin chip resistor page.

The short version

The 1225 chip resistor size is written two ways in Walsin’s chip resistor export, and only one of them is arithmetically right. 1225(3264) appears on 1,708 rows, all Thick Film Wide Terminal Power. 1225(3263) appears on 47, all Metal Foil Low Ohm Power Sensing. 1225 imperial is 3.2 × 6.4 mm, fourteen other imperial codes in the same file map one-to-one, and 6.3 mm appears nowhere else in 234,815 rows. The two populations share no resistance value: the 47 span 0.0005 Ω to 0.025 Ω, the 1,708 span 0.1 Ω to 1 MΩ. So a filter on the correct code drops the entire sub-0.1 Ω range at that footprint, and every part at 1225 that reaches ≦±50 ppm/°C. We hold no datasheet for either series, so the conclusion is arithmetic and is flagged as such. Qualification stays with you.

Send us the shunts and wide terminal parts off your BOM and we will cross them on the imperial code, not the metric one — then tell you which candidates were in Hong Kong on 23 September 2026. And if your selector told you Walsin’s lowest 1225 resistance is 0.1 Ω, that is the 47 rows talking, and we would like to know which selector it was.

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Frequently asked questions

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