How to Select Proper Length for Solar Through Bolts?

Solar power stations are exposed to outdoor conditions all year round, suffering from wind, sunlight and temperature fluctuations. Some projects face salt spray and rain erosion. The selection of bolts directly determines the service life and safety of solar mounting structures. Many buyers overlook material strength and length matching, which may lead to loosening and corrosion in later operation.

1. Product Introduction

This solar through bolt is a combined fastener specially designed for rooftop solar systems. The full set consists of fully threaded stud, square metal pressure plate, EPDM rubber composite waterproof washer and hex nut. It is a core component for solar mounting installation on metal roof panels. The stud adopts one-piece forming process with precision rolled threads. The full and neat thread profile ensures tight engagement and prevents thread slipping. The matched square pressure plate enlarges the bearing area and disperses local pressure to avoid roof panel deformation. Paired with our self-developed EPDM composite washer, it realizes integrated fastening and waterproof sealing.

2. Material Selection: A2-70 Stainless Steel 304

Our solar through bolts are made of stainless steel 304 with grade A2-70. A2 stands for 304 stainless steel, and 70 refers to minimum tensile strength of 700MPa. It balances mechanical strength and corrosion resistance, suitable for open-air environments to resist moisture and mild salt spray, and reduces maintenance cost. Ordinary carbon steel bolts are not recommended for outdoor solar projects due to high rust risk.

3. Length Selection: Available M10 Sizes

We supply M10 solar through bolts in 3 common stock lengths: M10×200, M10×250, M10×275.

· M10×200: For thin sheet & thin base with small assembly thickness

· M10×250: Universal size for most rooftop solar projects

· M10×275: For roof with thick insulation layer and thick panels

4. Structural Advantage with EPDM Composite Washers 

Each bolt set includes square metal plate and EPDM composite washer. When tightened, the rubber gasket fits tightly on roof panels to achieve waterproof sealing, preventing water leakage through bolt holes, combining fastening and waterproof functions for metal rooftop solar installation. EPDM washer features excellent aging and ozone resistance, resisting hardening and cracking under long-time sun exposure to maintain stable sealing performance.

5. Selection Reminders

• For coastal areas with heavy salt spray, higher corrosion-resistant material is available as upgrade option.
• Control tightening torque during installation to avoid roof panel damage.
• Calculate total sandwich thickness before ordering to select proper bolt length.

Jiaxing Aoke Hardware has decades of experience in solar fastener supply and own mature supply chain resources and a complete quality control system. With full-chain risk assessment capability, we steadily control quality and lead time, and deliver one-stop service including technical selection support, mass supply and after-sales technical consultation. We are your reliable partner for fastening and sealing solutions for global photovoltaic projects.