Grade 5 vs Class 8.8 Hex Cap Screws: Which Grade Fits?

Quick answer

Choose SAE Grade 5 when your equipment uses inch threads and you need a familiar, moderate-strength fastener; choose metric Class 8.8 when the mating nut or tapped hole is metric and you want a higher nominal strength class. The thread system, not the grade label, is the first decision.

Thread system decides compatibility before strength does

A 7/16-14 screw will not thread into an M8-1.25 hole, and an M8-1.25 screw will not thread into a 7/16-14 nut. Before comparing grades, confirm whether the assembly is inch or metric. The supplied options show this clearly: the Grade 5 screw uses a 7/16-14 inch thread, while the Class 8.8 screw uses an M8-1.25 metric thread.

Mixing systems with adapters or forcing threads damages both the fastener and the joint. If your equipment manual lists inch sizes, stay with SAE; if it lists metric sizes, stay with metric.

Strength class and what it means for your joint

Grade 5 and Class 8.8 are both moderate-strength grades, but they come from different standards. Class 8.8 is a metric property class with a specified nominal tensile strength, while Grade 5 is an SAE grade with its own strength requirements. The catalog does not list exact tensile values for either product, so use the grade labels as a starting point and verify against your engineering specification when the joint is safety-critical.

In practice, Class 8.8 often provides a higher nominal strength than Grade 5 for a comparable size, but the difference only matters if the joint is designed around it. For general machinery and equipment assembly, either grade can work when the thread system and size match the design.

Finish, thread style and pack size trade-offs

Both products use a yellow zinc CR+6 finish and are fully threaded. Yellow zinc offers mild corrosion protection for indoor and sheltered applications, but it is not a substitute for stainless or hot-dip galvanized fasteners in wet or outdoor environments. Fully threaded screws are versatile for clamping across their length, but they have less unthreaded shank than partially threaded alternatives.

Pack size is another practical difference: the Class 8.8 screws come in packs of 1,500, while the Grade 5 screws come in packs of 650. Higher volume lowers the per-piece cost but ties up more capital and storage space. Match the pack to your consumption rate rather than chasing the lowest unit price.

Trade-offs to weigh before you buy

• Thread system compatibility: Match the screw thread to the nut or tapped hole: 7/16-14 for inch assemblies, M8-1.25 for metric assemblies. Never force a mismatched thread. Check the equipment manual or existing fastener before ordering.
• Strength class vs application: Class 8.8 generally offers higher nominal strength than Grade 5, but exact values are not in the catalog. For safety-critical joints, confirm the required grade with your engineer. Do not substitute grades without verifying the joint design.
• Pack size vs consumption: The Class 8.8 pack contains 1,500 pieces; the Grade 5 pack contains 650. Choose the pack that matches your usage rate to avoid excess inventory or frequent reordering. Calculate monthly usage before committing to a bulk pack.

Product facts

• M8-1.25 X 18mm Hex Head Cap Screws | Class 8.8 Steel Yellow Zinc | Fully Threaded (1500 / Pkg.): M8-1.25 x 18mm, Class 8.8 steel, yellow zinc CR+6, fully threaded, 1,500 per pack. A metric Class 8.8 option for M8-1.25 assemblies, supplied in high-volume packs for repeated production use.

  

• 7/16-14 X 1" Hex Head Cap Screws | Grade 5 Steel Yellow Zinc | Fully Threaded (650 / Pkg.): 7/16-14 x 1 inch, Grade 5 steel, yellow zinc CR+6, fully threaded, 650 per pack. An inch-series Grade 5 option for 7/16-14 joints, with a smaller pack size that suits lower-volume or mixed-size inventories.

  

Which grade fits your job?

Best for

• Inch-based machinery and equipment that specifies 7/16-14 fasteners
• General assembly where a familiar SAE Grade 5 fastener is acceptable
• Maintenance teams that stock inch-series hardware

Not for

• Metric assemblies that require M8-1.25 threads
• Applications needing a higher strength class than Grade 5 or Class 8.8
• Wet or outdoor environments where yellow zinc corrosion protection is insufficient