Grog Splice Full Break Tests

Last updated December 15, 2024.

• Grog splices
• Split connections
• Breaktests

These are the unedited values for the 20 breaktests of grog splices completed in June 2022. The tests were done with Jerry Miszewski, owner of Balance Community Slacklines, in the Balance Community shop. All splices were made and installed in the machine by me. All tests were made on Amsteel Blue, purchased by me in 2021, except for the silver Amsteel provided by Jerry (used in the 6" used tests, and the one pictured in the preliminary testing section) and blue Amsteel purchased by me in 2020 (used in the other two preliminary tests).

The final four entries with a single asterisk were all used. The extent of use is described more in the main article.

The 5" grog with asterisks on the side got caught in the threads of the shackle pin and tore open. After that point we switched from attaching grogs at the pin to attaching them at the bow.

This section covers tests done since the main tests listed above. The tests were done with Jerry Miszewski, owner of Balance Community Slacklines, in the Balance Community shop. All tests were made on Amsteel Blue unless otherwise stated. All tests have 4" bury lengths unless otherwise stated.

Single wrapped grogs made with 4mm dyneema.

Double wrapped grogs made with 4mm dyneema.

Double wrapped grogs made with 5mm dyneema.

Grogs with both tails spliced into the hole created on their respective side of the brummel.

Grogs made from New England Ropes Endura 12 instead of Amsteel Blue.

Before the main tests above, three different preliminary tests were done. These are discussed below. These tests are all characterized by low sample numbers and a lack of controls.

I first tested grog splices with Jerry in August of 2021, again in the Balance Community workshop. We tested three grogs, two I had premade and one I made on site. All were 5mm dyneema, but unfortunately we did not measure the bury lengths. One of the premade grogs was made of used dyneema from a Snatch whose splice had failed. That test failed the lowest. Oddly, the other two values are quite a bit higher than normal when compared to the larger testing done a year later on the same test machine.

Before first using the grogs I had made at the Fruit Bowl for Halloween 2021, we decided to try break testing them in the parking lot to make sure the 4" bury size I had chosen was sufficient. We pulled the grogs between a van and a large pickup truck, using a Linescale 2 to read the values. We were able to pull up to 21.5 kN, which convinced us they were safe enough to rig at the festival. We could not break a 4" bury grog, but we experimented with unburying one or both tails to see if we could force a failure. Using both tails unburied causes the brummel to invert and fail at extremely low forces. We didn’t get a good reading, but it was nearly immediate. With only one of the two tails buried, the dyneema in the unburied tail fully unravels causing the brummel to come undone and the loop to fail around 15 kN. One tail appears to be slightly stronger than the other.

Here is an inverted brummel from not burying either tail:

Here is a fully unwoven tail from burying only one tail:

Jake Monaghan heard about using grogs and wanted to test, but only had access to a pulley system. So he used 7/64" dyneema in hopes of being able to scale up the test results to 5mm dyneema. His findings are below.

I will be trying to keep this page up to date with feedback and new information, and will keep track of edits as I make them here.

1. Specified “Amsteel Blue” as the dyneema typed used in breaktests, and the source of the different dyneema used (7/18/22).
2. Specified which tests in the main table were used grogs (7/18/22).
3. Added the “Additional Testing” section to reflect tests made in spring of 2023 (5/11/23)