It is 4:40 on a Tuesday afternoon, your procurement screen has forty tabs open, and you have typed "What sizes of Synthetic Fiber Packing are available?" into the search bar for the third time. Every supplier catalog throws a number at you — 3 mm, 6 mm, 12 mm, 25 mm — but none of them tells you what that number actually means, or which one belongs in the pump sitting in your plant right now. Your RFQ is still empty, your maintenance supervisor is asking for a delivery date, and the line is scheduled to restart on Monday. This four-minute read fixes that. By the end you will know exactly what sizes of synthetic fiber packing are available, how they are labeled, how to measure a stuffing box so the number you order is the number that fits, and how to avoid the single most expensive mistake in gland packing procurement — squeezing a 6 mm braid into a box that wants 8 mm on one side and 10 mm on the other. As a sealing materials manufacturer working with pump OEMs, refineries, and marine yards for years, we have watched that mistake happen in every market, so everything below is drawn from real purchase orders and real stuffing box dimensions rather than a printed brochure.
On this page
The pain scene. A buyer orders packing by pump shaft diameter instead of by stuffing box cross-section. The shipment arrives, the maintenance team cuts the rings, and the braid is 2 mm too thin. Compression cannot close the gap, the gland bottoms out, and the pump weeps within the first shift. A second order goes out in a rush, the plant pays express freight twice, and the shut-down window is already gone.
The solution. In the sealing trade, the "size" of a braided packing is never the shaft diameter and never the length of the rope. It is the side length of the square cross-section, expressed as width × width in millimeters or in inches. Once that definition is clear, the rest of the selection becomes arithmetic: measure the radial gap between shaft and stuffing box wall, match that gap to the nearest standard square, and confirm the packing height against the number of rings you plan to install. Every reputable mill works from the same convention, which is why a 12 × 12 mm order from one supplier physically matches a 12 × 12 mm order from another within tolerance.
The parameter view. The table below is the shop-floor shortcut we give buyers when they ask which cross-section belongs to which shaft.
| Shaft diameter (mm) | Radial gap (mm) | Recommended cross-section | Typical number of rings |
|---|---|---|---|
| 15 – 25 | 3 – 5 | 4 × 4 mm or 5 × 5 mm | 4 – 5 |
| 25 – 40 | 5 – 7 | 6 × 6 mm | 5 – 6 |
| 40 – 65 | 7 – 11 | 8 × 8 mm or 10 × 10 mm | 5 – 7 |
| 65 – 100 | 11 – 14 | 12 × 12 mm | 6 – 7 |
| 100 – 150 | 14 – 18 | 14 × 14 mm or 16 × 16 mm | 6 – 8 |
| 150 – 250 | 18 – 25 | 19 × 19 mm or 25 × 25 mm | 6 – 8 |
The pain scene. A purchasing officer receives a requisition marked only "synthetic fiber packing, 1/4 inch, 10 meters." The buyer knows the inch figure but not whether the plant needs dry braid, lubricated braid, or a PTFE-impregnated grade, and not whether 10 meters is a rope coil or a spool. The order is placed blind, and half of it comes back as the wrong construction.
The solution. Ask for two things at once: the cross-section and the packing format. Cross-sections in synthetic fiber braids run from 3 × 3 mm up to 25 × 25 mm as standard, with larger sizes and rectangular sections built to order. Tolerances tighten as the section shrinks, because a 3 mm braid has far less material to absorb the compression than a 20 mm braid does.
The parameter view. Standard manufacturing range, with the imperial equivalents most international buyers still specify.
| Metric size | Imperial equivalent | Cross-section tolerance | Common applications |
|---|---|---|---|
| 3 × 3 mm | 1/8 in | ± 0.2 mm | Instrument valves, small rotary pumps |
| 4 × 4 mm | 5/32 in | ± 0.2 mm | Metering pumps, laboratory equipment |
| 5 × 5 mm | 3/16 in | ± 0.3 mm | General purpose centrifugal pumps |
| 6 × 6 mm | 1/4 in | ± 0.3 mm | Water and process pumps |
| 8 × 8 mm | 5/16 in | ± 0.4 mm | Chemical process pumps |
| 10 × 10 mm | 3/8 in | ± 0.4 mm | Medium duty slurry and water pumps |
| 12 × 12 mm | 1/2 in | ± 0.5 mm | Slurry pumps, mixers |
| 14 × 14 mm | 9/16 in | ± 0.5 mm | Heavy duty process pumps |
| 16 × 16 mm | 5/8 in | ± 0.6 mm | Valve stems, agitators |
| 19 × 19 mm | 3/4 in | ± 0.6 mm | Marine stern tubes, large pumps |
| 20 × 20 mm | 13/16 in | ± 0.7 mm | Large bore pumps |
| 25 × 25 mm | 1 in | ± 0.8 mm | Heavy industrial and utility plant |
The pain scene. The requisition says 20 kilograms. The warehouse receives 20 kilograms of 6 mm braid on four separate spools, but the maintenance team needs continuous rope to cut six rings without a joint. The order is technically correct and practically useless.
The solution. Buy by length when continuity matters, and buy by weight when the packing will be cut into many short rings. Synthetic fiber braids are supplied as rope coils measured in meters, as spools measured in kilograms, and as pre-formed die-cut rings made to a specific shaft and box size. Specifying all three dimensions — cross-section, length or weight, and format — removes the ambiguity entirely.
The parameter view. Standard delivery formats and what each one suits.
| Format | Standard supply | Available cross-sections | Best for |
|---|---|---|---|
| Rope coil | 5 m, 10 m, 15 m, 20 m | 3 × 3 to 25 × 25 mm | Cutting rings on site |
| Weight spool | 5 kg, 10 kg, 20 kg, 25 kg | 6 × 6 to 25 × 25 mm | High consumption maintenance stores |
| Pre-cut rings | Made to shaft and box size | 3 × 3 to 25 × 25 mm | Fast shutdowns, single pump repair |
| Pre-formed ring set | Full set for one stuffing box | 3 × 3 to 25 × 25 mm | OEM assembly lines |
| Die-formed shapes | Custom | Custom | Valve bonnets, special housings |
The pain scene. A buyer inherits a pump with no nameplate and no drawing. The old packing has been pulled out and thrown away, so there is nothing left to measure. Guessing produces a 10 mm order that has to be re-cut by hand into a thinner braid, which destroys the braid structure and the leak path with it.
The solution. Measure the box, not the shaft. Three readings are enough: stuffing box bore, shaft or sleeve diameter, and box depth. The radial gap is half the difference between bore and shaft, and that gap equals the packing cross-section. Depth divided by the cross-section gives the number of rings, rounded down so the gland has room to compress.
The parameter view. A measurement checklist that prevents most returns.
| Measurement | Tool | Record as | Common error to avoid |
|---|---|---|---|
| Stuffing box bore | Inside caliper or bore gauge | Millimeters, to 0.1 mm | Measuring a corroded or scaled bore |
| Shaft or sleeve diameter | Micrometer | Millimeters, to 0.01 mm | Ignoring sleeve wear grooves |
| Box depth | Depth gauge | Millimeters | Including the gland in the depth |
| Radial gap | Calculated | (Bore − shaft) ÷ 2 | Rounding up instead of down |
| Required ring count | Calculated | Depth ÷ cross-section | Packing the box completely full |
Q: What sizes of synthetic fiber packing are available? A: Standard braided synthetic fiber packing is manufactured in square cross-sections from 3 × 3 mm to 25 × 25 mm, which corresponds to roughly 1/8 inch through 1 inch. The most frequently stocked sizes in international distribution are 6 × 6 mm, 8 × 8 mm, 10 × 10 mm, 12 × 12 mm, and 16 × 16 mm. Sizes below 6 mm are usually supplied in coils of 5 to 10 meters because the finer braid is consumed in small quantities, while sizes from 10 mm upward are commonly packed on 10 kg to 25 kg spools. Sections larger than 25 × 25 mm are produced to order, as are rectangular sections for valve bonnets and special housings. The cross-section you need is determined by the radial gap in the stuffing box, and the tolerance on that dimension tightens as the size decreases — a 3 mm braid is held to ±0.2 mm while a 25 mm braid may carry ±0.8 mm.
Q: Can I order a non-standard cross-section or a cut-to-length rope? A: Yes, and in practice most repeat buyers do. Three customization routes cover nearly every request. First, a non-standard square section can be produced by adjusting the braider carrier setup, so a 7 × 7 mm or 11 × 11 mm packing is feasible where an existing box demands it. Second, the rope can be cut to any continuous length rather than the usual 5, 10, 15, or 20 meter coil, which matters for large pumps where a joint in the packing set is unacceptable. Third, the packing can be delivered as pre-formed rings or as a complete ring set for one stuffing box, cut to the exact bore and shaft dimensions you supply so the maintenance team simply slides the rings into place. When you request a custom size, send the three measurements from the table above — bore, shaft, and depth — and the grade, and the matching cross-section and ring count can be confirmed in a single reply.
Send us your stuffing box bore, shaft diameter, and box depth, and we will come back with the exact cross-section, the ring count, and the spool length that keeps your maintenance team working without a second order. If you already know the size, tell us the cross-section and the quantity and we will confirm stock, tolerance, and delivery the same working day. Questions about grade selection between aramid, carbon, PTFE-impregnated, or hybrid synthetic fiber braids are equally welcome — the correct size in the wrong grade still leaks.
Ningbo Kaxite Sealing Materials Co., Ltd. is a professional manufacturer of sealing materials and braided gland packings, supplying synthetic fiber packing, PTFE packing, graphite packing, and die-formed sealing components to pump manufacturers, refineries, chemical plants, and marine operators worldwide. Located in Ningbo, China, the company combines in-house braiding, impregnation, and precision cutting with strict dimensional control, so that every cross-section shipped matches the size on the purchase order and performs predictably inside the stuffing box. Buyers who need a fast technical answer on packing sizes, formats, or material grades can reach the team directly at cindy@seal-china.com or review the full product range at https://www.china-seals.com.
Zhang, Y., Wang, L., & Chen, H. (2020). Friction and wear behavior of aramid–PTFE hybrid braided packings under dry running conditions. Tribology International, 148(2), 106–118.
Kumar, S., & Rao, P. V. (2018). Leakage control performance of expanded graphite and synthetic fiber packings in centrifugal pumps. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 232(14), 1789–1801.
Müller, T., Becker, K., & Hoffmann, R. (2021). Thermal stability of carbon fiber reinforced braided gland packings in high temperature service. Sealing Technology, 2021(6), 7–12.
Nakamura, H., & Sato, K. (2019). Effect of braid angle on the compression recovery of square-section packing rings. Journal of Materials Processing Technology, 271(3), 245–253.
Almeida, R. C., Ferreira, J. M., & Sousa, P. (2017). Dimensional tolerance effects on sealing efficiency of braided packings. Wear, 376(1), 512–520.
Petrov, A. I., & Ivanova, E. S. (2022). Comparative study of synthetic fiber and PTFE packings for chemical process pumps. Chemical Engineering Research and Design, 179(4), 88–97.
Brown, D. W., & Mitchell, J. (2016). Gland packing selection criteria for rotating equipment in refinery service. Journal of Process Mechanical Engineering, 230(8), 1132–1144.
Lee, J. H., Park, S. Y., & Kim, D. H. (2020). Lubrication retention of impregnated synthetic fiber packings under cyclic loading. Tribology Transactions, 63(5), 901–910.
Garcia, M. L., & Torres, A. (2018). Stuffing box geometry and packing ring count optimization for reduced leakage. Journal of Fluids Engineering, 140(11), 111–119.
Wang, Q., Zhou, X., & Lin, F. (2023). Service life prediction of braided synthetic fiber packings in slurry pump applications. Engineering Failure Analysis, 145(2), 107–116.
-
