Star plates, also known as truss connector plates, gang-nail plates, or metal connector plates, are stamped metal plates used to connect wood framing members at critical joints in engineered trusses and framing systems. Despite their simple appearance, these connectors are sophisticated engineered components that play a significant role in the structural integrity of modern light-frame construction. Each plate is designed to resist specific combinations of tension, compression, and shear forces at the joint. This comprehensive guide covers the different types of star plates, their load-rated applications, proper installation procedures, engineering standards, and how to identify them on existing structures.
What Are Star Plates?
Star plates are galvanized steel plates with integral teeth or prongs that are pressed into wood members to create a strong mechanical connection. The name derives from the starburst pattern of teeth that radiates from the center of the plate, though modern plates may have various tooth patterns optimized for specific loading conditions. These connectors are manufactured by cold-stamping 16-gauge to 20-gauge galvanized steel sheet, which produces the teeth and simultaneously forms them at right angles to the plate surface. The stamping process work-hardens the steel, increasing its yield strength in the tooth area.
The plates function by embedding their teeth into adjoining wood members, creating a connection that resists both tension and shear forces. Unlike nails or screws that fasten through one member into another, star plates provide surface-level grip across a broad area, distributing loads more evenly across the joint interface. Each tooth creates an individual stress field in the wood, and the collective action of all the teeth produces the overall joint strength.
| Star Plate Category | Typical Dimensions | Steel Gauge | Tooth Count Range | Primary Application |
|---|---|---|---|---|
| Standard truss plate | 3 in × 5 in to 4 in × 6 in | 18 ga (0.048 in) | 20 – 40 | Pre-engineered roof trusses |
| Heavy-duty truss plate | 4 in × 8 in to 6 in × 10 in | 16 ga (0.060 in) | 40 – 80 | Floor trusses, heavy beam connections |
| Mini connector | 1.5 in × 3 in to 2 in × 4 in | 20 ga (0.036 in) | 8 – 16 | Light framing, bracing, retrofit repairs |
| Gusset plate (punched) | 6 in × 6 in to 12 in × 12 in | 14 ga (0.075 in) | 60 – 150+ | Structural splice connections, large trusses |
Historical Context and Development
Star plates emerged in the mid-20th century alongside the development of engineered wood trusses. Before their introduction, wood truss joints were connected with plywood gusset plates glued and nailed in place, a labor-intensive process that limited truss production. The pressed-metal connector plate was patented by John C. Jureit in 1952, and his company Gang-Nail Systems Inc. became the dominant manufacturer. The pressed-metal plate drastically simplified truss manufacturing, enabling the growth of the pre-fabricated truss industry.
By the 1970s, essentially all factory-built roof trusses used metal connector plates. Today, the Structural Building Components Association (SBCA) reports that over 80 percent of residential roof structures in the United States utilize metal-plate-connected (MPC) trusses. The industry produces over 50 million roof trusses annually in North America, each containing an average of 15 to 25 connector plates.
Applications in Modern Construction
Roof Trusses
The most common application for star plates is in pre-engineered roof trusses. At each joint where web members meet chords, truss plates transfer tensile and compressive loads between members. The design of each plate location is calculated by truss design software (such as MiTek or Alpine), which specifies the exact plate size, orientation, and number of teeth required to handle the design loads. Each truss joint is unique and may require a different plate configuration depending on the load path through that joint.
Floor Trusses
Floor trusses use larger heavy-duty plates because the dead and live loads are generally higher than in roof applications. Floor trusses span between bearing walls or beams, creating open spaces for mechanical systems. The plates at the top and bottom chord connections must resist both gravity loads and diaphragm shear forces. Heavy-duty plates with deeper tooth penetration (typically 0.375 inch compared to 0.250 inch for standard plates) are used to achieve the required load ratings.
Retrofit and Repair
Star plates are also used in retrofit applications where existing connections need reinforcement. Splice plates can repair damaged truss members resulting from cutting, water damage, or impact. Mini connectors can strengthen loose or undersized joints in existing framing. Building inspectors often require star-plate reinforcement when modifying load-bearing walls or cutting into existing trusses for roof penetrations such as skylights or HVAC ducts.
Engineering and Load Capacity
The load capacity of a star plate connection depends on several factors: the plate dimensions, tooth count and pattern, steel thickness, wood species and density, grain orientation, and the direction of the applied load relative to the plate. Each tooth has an allowable design value for lateral resistance (shear) and withdrawal (tension). These values are determined through standardized testing per ASTM D1761 and are published in the manufacturer’s code evaluation reports (ICC-ES ESR reports).
| Plate Size | Tooth Count | Allowable Tension (lb) | Allowable Shear (lb) | Max Wood MC |
|---|---|---|---|---|
| 3 in × 5 in | 24 | 1,200 | 1,800 | 19% |
| 4 in × 5 in | 32 | 1,600 | 2,400 | 19% |
| 4 in × 8 in | 52 | 2,600 | 3,900 | 18% |
| 6 in × 6 in | 60 | 3,000 | 4,500 | 18% |
| 6 in × 10 in | 90 | 4,500 | 6,750 | 16% |
Installation Requirements
Proper installation of star plates is critical to their structural performance. Manufacturer specifications and building codes mandate specific requirements:
- Press force: The plates must be pressed into the wood using a hydraulic or pneumatic press that delivers the manufacturer’s specified force (typically 2,000 to 8,000 pounds depending on plate size). Hammering is not an acceptable installation method because it cannot deliver uniform tooth penetration across the entire plate.
- Tooth embedment: Teeth must be fully embedded so the plate surface contacts the wood. Partial embedment reduces load capacity by up to 50 percent and creates a corrosion path between the plate and the wood.
- Wood moisture content: Truss plates should be installed in wood with a moisture content between 12 and 18 percent. Overly dry wood (below 10 percent) can crack during pressing. Overly wet wood (above 20 percent) does not provide adequate tooth grip and may shrink after installation, loosening the plate.
- Plate alignment: The plate must be centered on the joint line with equal coverage on both connecting members. Off-center installation creates eccentric loading that can cause joint failure under design loads.
Identification of Existing Star Plates
When working on an existing building, identifying the star plates in trusses helps determine load paths and assess structural modifications. Look for the galvanized steel plates at every truss joint. Each plate typically carries a manufacturer stamp or code that can be traced back to engineering specifications. The absence of plates at a joint that appears to be a truss connection may indicate a field repair or a non-engineered modification.
If you are cutting or drilling into a truss for a roof window, skylight, or mechanical penetration, avoid cutting through or near connector plates. Even a single severed plate tooth can reduce the joint capacity significantly. Many professional truss repair kits include star plates specifically designed to reinforce trusses that have been altered or damaged.
Corrosion Protection
Standard star plates are galvanized with a G60 or G90 zinc coating for corrosion resistance suitable for dry interior conditions. For exterior applications, pressure-treated wood connections, or high-humidity environments, stainless steel (304 or 316 grade) or hot-dip galvanized plates with G185 coating should be specified. The corrosion rate of standard G90 galvanized plates in interior service is negligible, but in coastal environments within 1 mile of salt water, or where the wood preservative contains copper (ACQ or CA-C treated lumber), the plate life can be significantly reduced — by as much as 50 percent over 10 years.
Understanding star plates is essential for anyone involved in wood frame construction. These simple pressed-metal connectors enable the efficient, cost-effective, and structurally sound truss systems that form the backbone of most residential and light-commercial construction today.