Editing Block and tackle (section)

== Mid-line attachment==
When installing a block on an existing line, it is often inconvenient at best to thread the rope through the block to be added.

*Open blocks have a space wide enough between the fixed cheeks to be able to slide the pulley over the rope. These can be extremely small and light while retaining significant strength due to the lack of moving parts.

*A swing cheek block is a special kind of block which can be opened to engage with a [[Bight (knot)|bight]], without the necessity to thread the rope through the block or remove the load from the end of the rope. The snatch block is also the load lifting pulley in certain arrangements, such as during use in a recovery operation.<ref>{{Cite web |url=https://blog.uscargocontrol.com/what-is-a-snatch-block/ |title=What is a Snatch Block? |last=Mathews |first=Lisa |date=2016-02-02 |website=US Cargo Control Blog |archive-url=https://web.archive.org/web/20191219100112/https://blog.uscargocontrol.com/what-is-a-snatch-block/ |archive-date=2019-12-19 |access-date=2019-12-19}}</ref>

[[File:Three snatch blocks.jpg|thumb|Three vintage snatch blocks showing the ‘snatch’ closed, opened, and securely moused]]

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Swing cheek blocks may be roughly divided into two categories:

* Swing cheek pulleys: used for light loads or redirection of forces, usually with a single pulley wheel (though multiple sheaves/cheeks are not uncommon) and an attachment point (or several) for a carabiner or sling. The cheeks are not fixed or locked in position aside from the device used to secure them to the load or rigging point. 
::Examples of use (in an arboricultural setting) include: tail minding/tending, and for setting a rigging point in the tree above the cut to take place—a positive rigging situation.

*Snatch or impact blocks: used for heavier loads and more dynamic rigging, the cheeks of these blocks are fixed in place with a pin which locks into the opposite cheek. This pin may form part of the axle for a second pulley, which is secured to the load or rigging point with a soft sling, rather than a solid device such as a shackle. This allows for more even distribution of forces to the faces where the forces will be applied, as opposed to a carabiner or shackle, where the forces are applied more strongly to corners and edges, increasing risk of deformation or damage.
::Examples of use (again, in relation to tree care) may include setting a block below the current cut, resulting in a 'negative' rigging situation, in which shock loads can be significant—especially if removing large sections of vertical stem.