Arborist Blocks

What makes an Arborist Block different?

All arborist blocks share features that set them apart from standard rigging pulleys:

• Upper sheave for sling attachment
• Widened cheek plates to protect ropes
• Large-diameter sheaves preserve rope strength

These features make a superior arborist block:

• Locking mechanism for upper sheave
• Rope-friendly, rounded surfaces
• More robust kN rating

Breaking Strength

Breaking Strength (Brk Str) is the force at which a device fails under test conditions. There are a few ways we list it here:

• Minimum Breaking Strength (MBS) - minimum load at which the device fails in testing.
• Average Breaking Strength (ABS) - average load at which the device fails in testing.
• Breaking Strength (Brk Str) - used when the manufacturer does not specify if the rating is minimum or average.

Working Load Limits

Working Load Limit (WLL) is the largest load a device is intended to handle, based upon the design factor - the ratio of breaking strength to working load.

• 5:1 - A generally-accepted ratio of load force to breaking strength in static hardware. (That is, where the load does not free fall.)
• 10:1 - This more conservative guideline is widely used in tree work to account for the multiplication of forces when a load must free-fall before being caught by the system. (Such as in removal of trunk wood.)

The ratings on some arborist blocks are extremely impressive. It is still better to try and minimize the forces your rigging system endures. Repeated loading can weaken systems.

It is the responsibility of the user to ensure rigging equipment is used within design specifications and manufacturer ratings. See ANSI Z133-2017 8.5.5