AMT's Low Mass Self-Centering Tension Screw

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Several ResoNation members have requested more info about AMT's unique "Low Mass Self-Centering Tension Screw" so here's a couple photos showing what it looks like.  Although it may not be apparent in these photos, the screw's head has a tapered base which forces it to 'self center' when installed into a countersunk hole in the spiderbridge's base.  It also has a double-slotted head that enables cone tension to be adjusted in 7, 8 or 10 string resos having a one-piece bridge insert (without a tension screw access gap in the center).

Part of the reason this screw has considerably less mass than a traditional tension screw is that it's much shorter; the extra length of a standard tension screw isn't required because the AMT screw is intended to be used only with a spiderbridge in which the screw's head makes direct contact with the spider's base, rather than the top edges of its bridge insert slot.

Reduced diameter of the upper portion of the screw's shaft, combined with its self-centering head design, prevents undesirable rattling/buzzing of the screw's shaft against the hole thru the spider's base -- which can easily occur with a standard tension screw if the spider isn't perfectly centered on the cone (especially if installed in a #14-style spider in the traditional manner, with its head resting on the upper edges of the bridge insert slot).






Sam Cassady's picture

What metal is used: brass, steel, aluminum?

The tension screw shown in the photos above is made of stainless steel, which is both stronger and lighter than brass.  If some inquisitive resoist wanted to try one of these screws made of brass I could certainly make them one, and it'd be MUCH easier to machine than stainless steel; however, it'd also be far more prone to bending and/or marring.  I'll probably eventually make a few out of brass just to see if I can hear any differences in how it sounds versus stainless (though I'd expect any differences to be barely noticeable, if at all).

Aluminum screws don't have suitable strength, rigidity, hardness or sonic transfer properties for use as a reso tension screw; they also aren't generally available in a 4-40 size (6-32 is the smallest size that's readily available).

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