How to Pair Tension Links with the Right Bolts and Retainers
Key Takeaway: Every tension link requires purpose-built bolts and retainers — standard hardware is not compatible. Use standard bolts for strokes ≤50 mm, urethane-wrapped bolts for longer strokes or high-speed cycling, single-flange retainers for standard loads, and double-flange retainers for heavy plates.
Why Standard Hardware Won't Work
Tension link bolts are specifically designed for repeated impact loading at the end-of-stroke contact. They differ from standard hardware in three ways:
- Material: Alloy steel, heat-treated for impact fatigue resistance — standard bolts are not rated for cyclic impact.
- Head geometry: Designed to sit within the oval hole with precise clearance — standard bolt heads are too thick or too thin.
- Surface treatment: Ground and polished contact surfaces to minimize friction as the bolt slides in the oval hole.
Bolt Selection Matrix
| Application | Bolt Type | Key Feature |
|---|---|---|
| Standard (≤50 mm stroke, ≤15 cpm) | Standard TL bolt | Heat-treated alloy steel, ground head |
| Long stroke (>50 mm) or high speed (>15 cpm) | Urethane-wrapped TL bolt | Urethane ring absorbs end-of-stroke impact |
Urethane-wrapped bolts reduce end-of-stroke noise by 10-15 dB and extend both bolt and link body life by absorbing the impact energy that would otherwise transfer to the metal surfaces.
Retainer Selection
| Retainer Type | Flange Count | Load Rating | Best For |
|---|---|---|---|
| Single Flange | 1 | Standard | Most applications, standard plate weights |
| Double Flange | 2 | High | Heavy plates (>200 kg), high acceleration opening |
The retainer mounts to the plate and holds the tension link bolt in position. Double-flange retainers distribute the stroke-stop force over a larger plate area, preventing localized deformation under heavy loads.
Frequently Asked Questions
Can I use any M12 bolt in a tension link?+
No. Tension link bolts are specifically designed for cyclic impact loading with precision head geometry. Standard M12 bolts lack the heat treatment, surface finish, and head dimensions required. Using standard bolts risks premature failure and mold damage.
When are urethane-wrapped bolts worth the extra cost?+
When stroke exceeds 50 mm (higher impact energy at end-of-stroke), cycle rate exceeds 15 cycles/minute (more impacts per hour), or noise reduction is important. The urethane wrapping typically doubles bolt life and reduces noise by 10-15 dB.
What is the difference between single and double flange retainers?+
Single flange retainers have one bearing surface for the bolt. Double flange retainers have two, distributing the end-of-stroke force over a larger area. Use double flange for plates >200 kg or when high-acceleration opening creates large impact forces.