t-terminal/t ball spin halyard block for gen 1 mast

[Tom Desmond]

Hello everyone,
Can't find my t-terminal spin halyard block.  Does anyone have a spare, know where I can buy a new one, or have an alternative setup that would work.  Any help would be greatly appreciated!

[Justin S]

Working with Tom and getting to a solution.

The spinnaker halyard exit on the Mark 1 masts was really nice. There is considerably less friction in the hoist and dowse, and the swivel block allows the top of the chute to rotate nicely.

It requires careful maintenance of the T fitting and swivel block, which should be held in place with the rubber stop when sailing to avoid any risk of coming out.
Then I recommend taking it off the mast to travel etc.

There has never been a better set up before or since, but the Mark 1 masts were all one-piece.  The Mark 1 masts also came with the favored cleat on a plate on the back of the mast for spin halyard as standard.  That was in the day when Superspar was owned by a sailor and the lads at the shop were riggers' riggers. 😇

[Jake Vick]

Any luck Tom?

This is what I found.    A Seldon T-eye Toggle, probably with a Harken 29mm Carbo T2 Soft-Attach Block.  And dont forget the retaining bung!

For the Viper 640 mast (whether you have the aluminum Proctor/Seldén mast or the carbon Superspar/Southern Spars mast), there is no off-the-shelf single block that comes molded directly onto a rigid T-bar fitting out of the box. [1, 2]
Instead, the class-standard way to rig a block into those specific 90-degree internal mast slots is a two-piece combination: a standalone stainless steel T-Terminal Eye Toggle / Loop paired with a modern lash-on block. This provides maximum articulating freedom so the block can align perfectly with line loads without binding or cracking the mast's internal backing plate. [3, 4, 5]
## 1. The Mast Attachment (The T-Bar)
You will need a standard wire-to-rope conversion T-terminal eye toggle (often called a loop terminal). Because Seldén components require precise matching to avoid cracking the internal backing plates, select the terminal corresponding to your mast manufacturer: [4, 5]

*
* Seldén Masts: Use a Seldén T-Eye Toggle (typically the 3mm or 4mm pin equivalents depending on the backing plate slot size).
* Superspar Masts: Use a matching Super Spars T-Terminal Wire Loop.
* Installation Note: Slip the T-bar horizontally into the slot, rotate it 90 degrees to lock it vertically, and pop in a rubber Seldén T-Terminal Retaining Plug into the gap above it to keep it from accidentally sliding or shaking out when the lines go slack. [1, 2, 5, 6]
*

## 2. The Single Block (Harken T2 Series)
Once the T-bar loop is locked into the mast, you lash a Harken T2 Soft-Attach Block directly through the eye of the terminal. For a Viper 640 mast, the two most common sizes found on the deck layout are: [7, 8]

*
* Harken T2 40 mm Soft Attach Block H2149: The most versatile choice for high-load main halyards, 2:1 jib halyards, or heavy spinnaker setups. It handles up to 3/8" (10 mm) line diameters and offers a clean, low-profile fit against the spar. [5]
* Harken 29mm Carbo T2 Block: Ideal if you are rigging ultra-light high-performance lines, such as lazy jacks, small control lines, or low-load spinnaker halyard exits.
*

Are you setting this up for a 2:1 jib halyard, a spinnaker halyard lead, or something else? I can give you the exact lashing length suggestions and line paths based on what you are rigging.

[1] [https://www.superspars.com](https://www.superspars.com/SSlatest/mainpages/Productcodes.php)
[2] [https://www.ussailing.org](https://www.ussailing.org/wp-content/uploads/2020/09/Viper-640-Intl-Class-Rules-updated-January-1-2020-1.pdf)
[3] [https://westcoastsailing.net](https://westcoastsailing.net/parts/viper-640-sailboat-parts)
[4] [https://support.seldenmast.com](https://support.seldenmast.com/files/1681308368/595-950-E.pdf)
[5] [https://dinghy.seldenmast.com](https://dinghy.seldenmast.com/collections/t-terminals)
[6] [https://support.seldenmast.com](https://support.seldenmast.com/files/1681308368/595-950-E.pdf)
[7] [https://www.harken.com](https://www.harken.com/en/support/one-design-deck-layouts/viper-640/)
[8] [https://www.harken.com](https://www.harken.com/en/support/one-design-deck-layouts/viper-640/)

The exact names used by manufacturers and riggers for these small rubber inserts are:

*
* T-Terminal Retaining Plug (Official Seldén name)
* T-Terminal Rubber Bung
* T-Terminal Rubber Grommet [1]
*

## How They Work
When you insert a T-bar horizontally into the backing plate slot and twist it 90 degrees to lock it vertically, it drops down slightly under line load. This leaves a small empty rectangular void at the top of the mast slot. [2]
You push the rubber retaining plug directly into that top gap. It completely fills the void, acting as a physical wedge that locks the T-bar securely in place so it cannot accidentally lift up, rotate 90 degrees, and pop out of the mast when your halyard or control line goes completely slack. [3, 4]
## Available Options
Depending on your exact mast backing plate sizes, you can typically purchase them online:

*
* Selden T TERM RETAINING PLUG 2.5-3mm: The standard, most common size for dinghies and sportsboats like the Viper 640.
* Selden Rubber Plug T-Terminal Bung For Dinghy Masts: Individual replacements measuring roughly 6mm x 6mm to fit the standard backing plates. [2]
*

Are you missing just the rubber plugs, or do you also need to track down the stainless steel backing plates inside the mast slot?

[1] [https://sailboats.co.uk](https://sailboats.co.uk/products/selden-t-terminal-rubber)
[2] [https://binksmarine.com.au](https://binksmarine.com.au/collections/selden-mast-fittings)
[3] [https://www.tridentuk.com](https://www.tridentuk.com/gb/selden-t-terminal-retaining-plug-shroud-forestay.html)
[4] [https://dinghy.seldenmast.com](https://dinghy.seldenmast.com/products/t-terminal-retaining-plug)