Quad Doubles Serial Number
By Muhammad Khalid Hussain; published ; updated
Quad Doubles, also called Four Pairs, has four adjacent matching pairs in an eight-digit serial, such as 55998833. Banknote Expert checks the exact AABBCCDD shape and overlaps.
Enter your bill’s 8-digit serial number above to see its rarity score, any matched patterns and an estimated value range. Nothing is uploaded. The check runs entirely in your browser.
What is a quad doubles serial number?
Quad Doubles, the market name for Four Pairs, is an eight-digit serial with four adjacent matching pairs in the AABBCCDD shape. In 55998833, the pairs are 55, 99, 88 and 33. The pairs may repeat the same digit value elsewhere because the detector checks pair shape, not pair uniqueness.
Quad Doubles vs Double Quad and other doubles
Quad Doubles has four adjacent pairs, as in 11223344. Double Quad has four copies of one digit followed by four copies of another, as in 11112222. These names are easy to mix up, but their digit positions differ. Collectors also use doubles-family wording for serials with two, three or four adjacent pairs; the site's Four Pairs rule specifically requires all four pair positions.
| Name | Shape | Example |
|---|---|---|
| Doubles | A pair of equal adjacent digits | 11234567 |
| Tri Doubles | Three adjacent pairs | 11223345 |
| Quad Doubles / Four Pairs | Four adjacent pairs, AABBCCDD | 55998833 |
| Double Quad | Four of one digit then four of another, AAAABBBB | 11112222 |
Quad Doubles examples and non-examples
The detector asks whether positions one and two match, three and four match, five and six match, and seven and eight match. The four pair digits need not be distinct, pair order does not matter, and scattered non-adjacent repeats do not count. This allows overlaps such as Bookends in 11334411.
| Serial | Result |
|---|---|
| 55998833 | Four adjacent pairs; all pair digits distinct |
| 33000044 | Four adjacent pairs; pair values need not be distinct |
| 11223344 | Four pairs and ladder-four-pairs overlap |
| 11334411 | Four Pairs plus Bookends overlap |
| 11112222 | Double Quad, not Quad Doubles |
| 12121212 | Repeater, not adjacent pairs |
How rare is a quad doubles serial number?
Each of four adjacent pairs can independently use any of 10 digits, so there are 10^4 = 10,000 matching strings among 100,000,000 eight-digit strings. The detector odds are 1 in 10,000. The hub's previous 1 in 19,841 figure implicitly described a narrower case and did not match the current detector, which allows repeated pair values.
How much is a quad doubles note worth?
There is no publishable verified Four Pairs sold-price band in the current source. The condition table is blank, and no range is inferred from other pair patterns. Check completed sales for comparable notes before assigning a quad double value.
Use the fancy serial number value guide and confirm any star suffix with the star note lookup.
| Condition | Recorded range | Sample |
|---|---|---|
| Circulated | ||
| Very Fine | ||
| Uncirculated |
What raises or lowers a Quad Doubles note's value?
- A star note may add a separate collector feature, but no Quad Doubles star-note band is recorded.
- Binary pairs, a radar, a repeater or bookends can create additional pattern matches.
- Some buyers may prefer particular pair digits or order, but the site's sold data does not quantify those preferences.
- Denomination, condition and eye appeal affect comparable value. Compare notes with similar details.
Should you keep, sell, or grade a quad double?
The four-pair shape is easy to recognize, but no verified price band is available here. Keep it if you enjoy it or if strong overlaps and comparable completed sales support a premium. Consider grading only when condition and likely proceeds justify the full costs.
How to check your serial
Keep all eight digits and check the four adjacent pairs from left to right. Each pair must match internally. The pair values can repeat, and their order can vary.
Test the note in the fancy serial number checker and compare it with Bookends guide, Binary guide and Radar guide.
Check your serial on Banknote Expert
Enter all eight digits, including leading zeros, to see Quad Doubles and any overlapping patterns.
Open the fancy serial checkerQuad Doubles serial number FAQs
What is a quad double serial number?
An eight-digit serial arranged as four adjacent matching pairs, AABBCCDD. Collectors also call this Four Pairs.
What is the difference between a quad double and a double quad?
Quad Doubles alternates pair blocks such as 11223344. Double Quad has four identical digits followed by four of another digit, such as 11112222.
Do the pairs have to be next to each other?
Yes. Each matching pair must occupy adjacent positions in the AABBCCDD shape. Scattered equal digits do not meet this rule.
How rare is a quad double?
The detector allows any four pair digits, including repeats, giving 10,000 strings among 100,000,000, or 1 in 10,000.
How much is a quad double note worth?
No verified Four Pairs sold-price band is published in the current source. Compare completed sales for the same condition, denomination and overlapping patterns.