B16.21 Silicone Gasket
Manufacturer & Custom Solutions
Nonmetallic Flat Gaskets for Pipe Flanges
ZSR is a professional silicone gasket manufacturer. We produce flat gaskets according to ASME B16.21, including ring gaskets for raised face flanges and full face gaskets with bolt holes. Gaskets for this standard are usually made from compressed fiber sheet, PTFE or graphite. Silicone is a better choice when you need a wide temperature range from -60°C to +200°C, FDA food grade material, or good resistance to ozone and weather. Our gaskets fit ASME B16.5 flanges from Class 150 to Class 2500. Standard sizes are in stock, and custom sizes can be cut from your drawing. Send us your size list for a quick quote.
FDA 21 CFR 177.2600
Rubber Articles Intended for Repeated Use
LFGB 30&31
EU Food Contact Materials
USP Class VI / ISO 10993
Biocompatibility of Medical Devices
RoHS / REACH
Environmental Compliance
UL 94
Flammability of Plastic Materials
Built to Your Exact Spec
Custom Silicone Gaskets Options
| Image | Product | Type | Short Info | Action |
|---|---|---|---|---|
 | DIN 32676 Silicone Gasket | Standard & Size | DIN 32676 tri-clamp silicone gaskets, FDA food grade, full size range in stock at ZSR factory. | View Details |
 | AS568 Standard Silicone Gaskets | Standard & Size | AS568 standard-size silicone gaskets for groove-based sealing applications. | View Details |
 | DIN 3869 Silicone Sealing Ring | Standard & Size | DIN 3869 profile sealing rings in silicone for hydraulic ports, working from -60°C to +200°C. | View Details |
 | EN 1514-1 Silicone Gasket | Standard & Size | EN 1514-1 silicone flat gaskets for PN flanges, IBC and FF types, standard and custom sizes. | View Details |
 | Custom Die Cut Silicone Gaskets | Standard & Size | Flat silicone gaskets cut to any shape from sheet stock. Precision cutting for exact fits. | View Details |
 | ISO 7483 Silicone Gasket | Standard & Size | Silicone gaskets to ISO 7483 for ISO 7005 flanges, made for international projects and tenders. | View Details |
 | Custom Molded Silicone Gaskets | Standard & Size | Three-dimensional silicone gaskets made by compression or injection molding. For complex sealing shapes. | View Details |
 | ISO 1127 Silicone Gasket | Standard & Size | Sanitary silicone gaskets matched to ISO 1127 stainless steel tube sizes for food and pharma lines. | View Details |
 | Standard Flange Silicone Gaskets | Standard & Size | Silicone gaskets cut to fit pipe flanges. Matches ANSI, DIN and JIS bolt patterns. | View Details |
 | B16.21 Silicone Gasket | Standard & Size | ZSR makes silicone gaskets to ASME B16.21, ring type and full face type, for Class 150 to 2500 pipe flanges. | View Details |
 | ISO 2852 Silicone Gasket | Standard & Size | ISO 2852 silicone clamp gaskets for food industry couplings, FDA grade, factory direct from ZSR. | View Details |
 | Tri-Clamp / Sanitary Silicone Gaskets | Standard & Size | Hygienic silicone gaskets for food and pharmaceutical pipe connections. CIP and SIP compatible. | View Details |
 | B16.5 Silicone Gasket | Standard & Size | Silicone gaskets from ZSR sized to fit ASME B16.5 flanges, NPS 1/2 to 24 inch, Class 150 to 2500. | View Details |
 | Metric Size Silicone Gaskets | Standard & Size | Metric dimension silicone gaskets for international equipment standards. | View Details |
 | DIN 7603 Silicone Sealing Ring | Standard & Size | Flat silicone sealing rings made to DIN 7603 for screw plugs, banjo bolts and threaded fittings. | View Details |
 | DIN 2690 Silicone Gasket | Standard & Size | Silicone flat gaskets to DIN 2690 / EN 1514-1 dimensions for PN6 to PN40 flanges, food grade available. | View Details |
 | DIN 2691 Silicone Gasket | Standard & Size | Silicone gaskets made to DIN 2691 for tongue and groove flanges PN10 to PN160, ideal for plant repair. | View Details |
 | DIN 11851 Silicone Gasket | Standard & Size | Food grade silicone gaskets for DIN 11851 sanitary unions, DN10 to DN150, FDA material. | View Details |
 | FDA Food Grade Silicone Gasket | Grade | Food-safe silicone gaskets for processing equipment. FDA-compliant and taste-neutral. | View Details |
 | Medical Grade Silicone Gasket | Grade | Biocompatible silicone gaskets for medical devices. Sterilizable with full documentation. | View Details |
 | Industrial Grade Silicone Gasket | Grade | General-purpose silicone gaskets for industrial sealing. Reliable, durable and cost-effective. | View Details |
 | High Temperature / Heat Resistant Silicone Gaskets | Special Function | Heat-resistant silicone gaskets rated for continuous use above 200°C. For ovens and furnaces. | View Details |
 | Flame Retardant Silicone Gaskets | Special Function | Self-extinguishing silicone gaskets meeting UL 94 V-0. For fire-safety applications. | View Details |
 | Solid Silicone Rubber Gaskets | Materials | Solid silicone rubber gaskets with excellent compression set resistance and long service life. | View Details |
 | Fluorosilicone (FVMQ) Gaskets | Materials | Fuel and solvent-resistant silicone gaskets for chemical processing and automotive applications. | View Details |
 | Transparent / Clear Silicone Gaskets | Color | Clear silicone gaskets for visible sealing and light-transmitting applications. | View Details |
 | Black / White Silicone Gaskets | Color | Standard black and white silicone gaskets. Fastest delivery from stock. | View Details |
What ASME B16.21 Covers
ASME B16.21 is the U.S. standard for nonmetallic flat gaskets used between pipe flanges. When a flange follows ASME B16.5 (or the large-size B16.47), the gasket that goes between the flanges follows B16.21. The standard fixes the gasket's inner diameter, outer diameter, bolt hole pattern, and tolerances — so any gasket made to B16.21 fits its matching flange perfectly, no matter who made it.
The standard covers two gasket styles:
For tongue-and-groove flange facings, gasket dimensions follow the groove design — we also make these on request to the same size logic.
At ZSR Silicone Parts, we manufacture silicone B16.21 gaskets for NPS sizes from 1/2" to 24", and larger sizes (matching ASME B16.47 Series A and B flanges) on request.
Pressure Class and Dimensions
B16.21 gasket dimensions change with the flange pressure class — a Class 300 gasket has a larger outer diameter than a Class 150 gasket of the same pipe size. Here are the most requested sizes (ring type, dimensions in mm):
NPS | Class 150 ID × OD | Class 300 ID × OD | Standard Thickness |
|---|---|---|---|
1/2" | 21 × 48 | 21 × 54 | 1.5 / 3 mm |
3/4" | 27 × 57 | 27 × 67 | 1.5 / 3 mm |
1" | 33 × 67 | 33 × 73 | 1.5 / 3 mm |
1-1/2" | 48 × 86 | 48 × 95 | 1.5 / 3 mm |
2" | 60 × 105 | 60 × 111 | 1.5 / 3 mm |
3" | 89 × 137 | 89 × 149 | 1.5 / 3 mm |
4" | 114 × 175 | 114 × 181 | 1.5 / 3 mm |
6" | 168 × 222 | 168 × 251 | 1.5 / 3 mm |
8" | 219 × 279 | 219 × 308 | 1.5 / 3 mm |
10" | 273 × 340 | 273 × 362 | 1.5 / 3 mm |
12" | 324 × 410 | 324 × 422 | 1.5 / 3 mm |
Full charts for all sizes from 1/2" to 24", for Class 150 to Class 600, are available on request.
About higher pressure classes: silicone is a soft gasket material, and it performs best on Class 150 and Class 300 flanges. For Class 600 and above, we recommend thicker gaskets or our fiberglass reinforced silicone, which resists extrusion under high bolt loads.
Fast delivery
ZSR keeps cutting templates for all common B16.21 sizes on file — no template setup, no waiting. Standard sizes ship fast, and custom thicknesses or materials add only days, not weeks.
Material Options for B16.21 Gaskets
B16.21 fixes the dimensions — the material is your choice, and it should match your medium and conditions:
Material | Pressure Suitability | Temperature Range | Best For |
|---|---|---|---|
Solid Silicone (standard) | Class 150 – 300 | -60°C to +200°C | Water, steam, and air lines — the default choice |
Silicone Sponge | Low pressure only | -60°C to +200°C | Low bolt load flanges, plastic or glass-lined flanges, dust and splash sealing |
Fiberglass Reinforced Silicone | Class 150 – 600, high bolt load | -60°C to +230°C | High-temperature industrial flanges — no stretch, no extrusion, stable dimensions |
Fluorosilicone (FVMQ) | Class 150 – 300 | -60°C to +200°C | Fuel, oil, and solvent lines |
Our recommendation
For water, steam, and air service, choose solid silicone — it seals tight at low bolt load and outlasts EPDM and fiber sheet outdoors. For hot industrial flanges with heavy bolt loads, step up to fiberglass reinforced silicone. If the line carries fuel or oil, only FVMQ will hold up long-term.
Traditional B16.21 gaskets are made from compressed fiber sheet, PTFE, or graphite. Silicone beats them on temperature range, food safety, weather resistance, and ease of installation — especially on outdoor lines and food pipelines.
What Is ASME B16.21?
ASME B16.21 is an American standard published by the American Society of Mechanical Engineers. Its full title is Nonmetallic Flat Gaskets for Pipe Flanges. In plain words: it is the rulebook that defines the exact size of the flat, soft gaskets that sit between two bolted pipe flanges. First published decades ago and regularly updated, it is the standard that gasket buyers and flange makers across North America — and far beyond — work to every day.
Key Points of the Standard
