Stainless Steel Tubing – Slotted Square – 25 x 21mm x 5.8m

The 25 x 21mm square slotted tube is a purpose-designed top capping rail for frameless glass balustrade systems. Unlike the larger slotted profiles, this tube is not mounted on posts — instead, it sits directly on top of the glass panels, capping them with a continuous stainless steel rail that runs the full length of the balustrade.

The 21mm inner dimension of the profile is specifically engineered to accept 12mm glass with room for gaskets or silicone on either side, creating a secure, rattle-free fit. The result is a low-profile, highly refined finish where the rail appears to rest seamlessly on the glass — clean lines, minimal hardware, and a look that reads as professionally installed.

This profile is widely used in residential and commercial frameless glass installations across South Africa and is compatible with our full range of slotted square fittings, allowing corners and ends to be neatly mitred, joined, and capped.

Installation Notes

• Use neutral-cure silicone or clear rubber gaskets when fitting over 12mm glass for the best seal and a rattle-free finish — avoid acetoxy (acid-cure) silicone as it can stain stainless steel.
• Mitre, join, and cap as required for corners and ends using our matching 25 x 21mm square slotted fittings (sold separately): 90° fixed bends, adjustable bends, tube connectors, and end caps are all available in the Components & Fittings range.
• This profile is designed to be placed on top of glass panels — it is not a post-mounted top rail.
• No on-site welding is required for standard installations.

Specifications

• Profile: Square Slotted (Top Capping Rail)
• Dimensions: 25 x 21mm
• Slot Width: Designed for 12mm glass
• Length: 5.8m per piece
• Wall Thickness: 1.2mm
• Finish Options: Brushed Satin | Mirror Polish
• Grade Options: 304 Stainless Steel | 316 Marine Grade Stainless Steel
• Material: Stainless Steel
• Category: Stainless Steel Tubing – Slotted

Which Grade Should I Choose?

Grade 304 is strong and reliable, suited to internal applications and external use in non-coastal, non-corrosive environments — ideal for inland areas such as Johannesburg, Pretoria, and most non-coastal suburbs.

Grade 316 (Marine Grade) offers superior corrosion resistance and is the essential choice for coastal properties, poolside installations, and any environment exposed to salt air, moisture, or chemicals. If you are in Cape Town, the Winelands, Durban, or any coastal area, Grade 316 is strongly recommended.

Compatible Products

Pair this capping rail with our matching 25 x 21mm square slotted fittings — including 90° fixed bends, adjustable bends, tube connectors, and end caps — available in the Components & Fittings collection. Also pairs with our frameless glass spigots, stabilisers, and side-mounted bolts for a complete frameless glass system.

Tube Rolling & Fabrication

Our tube rolling service is available in-store at our Cape Town workshop. We can roll tubing to your required radius — ideal for curved handrails, sweeping deck railings, and architectural features. Round and slotted round tubing roll cleanly in most configurations. Square, rectangular, and slotted square or rectangular profiles can also be rolled, however these shapes are more complex and results will depend on the specific radius and application required — our team will advise you before proceeding. Contact us or submit a DIY Guidance request to discuss your project.

Not Sure What You Need?

Submit a free DIY Guidance request and one of our experts will review your project and confirm the exact products and quantities to order before you spend a single rand.