Frequently Asked Questions - will be updated as new questions are asked
- What is a TNT Gauge System, and what does it do?
The patented TNT Gauge Pro System is an accurate, durable, compact instrument for measuring the tension on a tennis net cord. The new "Pro" designation applies to all the models from 2012 forward, and indicates they are completely weather-resistant, and include a two-year manufacturer's warranty. It becomes a "System" when installed onto the passive net post by looping over an existing hook or bolting directly to the post, and working in conjunction with the posts and a strip of lubricating tape placed in the groove of post caps not equipped with a working pulley. When the net cord is tightened by the winding mechanism on the opposite post, and the simple calibration step is performed each day, the TNT Gauge accurately indicates the actual, in-line cord tension. By equalizing the tension on all courts at a facility, all the nets will play the same when a ball strikes the top of the net cord. A benefit for the facility is the knowledge that a net cord has not been over-tightened, which could cause damage over time to the net posts and their foundations.
How much do they cost, and how do I order TNT Gauge Pro Systems for my facility? How can I justify the cost?
TNT Gauge Pro Systems 2015 retail price is $119 each, with free shipping to US addresses, if ordered from Cable Tension, LLC. Note: The direct-mount, bolted model prices are $110 per court. Installation service is available.
Dealers: The TNT Gauge Pro System is only available from Cable Tension, LLC.
- Where can I download a summary presentation about the TNT Gauge and its benefits?
A January 2012 PDF presentation is here, and may be saved from the download.
- What Net Cord Tension is recommended?
January 2015: USTA publishes a revised Comment 1.1 to Rules of Tennis, Rule 1, with net tension recommendation that is equivalent to the ITF recommendation.
March 2014: USTA has joined ITF in recommending a tension of 400-450 pounds on the net cord, with all nets at a facility within 25 pounds of each other.
August 2012: The 2012 (and 2013, 2014) US Open will be playing doubles nets at 475 pounds; when they change to singles nets on 5 show courts, the nets will be set to 425 pounds. These tension settings are similar to those chosen by other pro tournaments.
July '11: For professional and championship play with normal nets, we recommend setting the TNT Gauge at 450-475 pounds for doubles. With Singles Sticks in place, set the tension at 400-425 pounds for the net to play equivalent to the doubles setting.
For recreational, league, and tournament play without Singles Sticks, we recommend using a setting of 425 pounds +/- 25. When using Singles Sticks at this level, a setting of 400 pounds is appropriate.
How does it work?
A TNT Gauge mounts to the outside of the "dead" net post (opposite one from the "crank" post) on each court, connecting in-line with the net cord's existing end loop. As the crank takes up the net cable and tightens the net, the cable force is redirected by the post's top cap down to the TNT Gauge, where a precision compression spring moves to accurately indicate the cable's actual tension across the system.
Installation, operation, and features of the TNT Gauge may be seen in a video at
this link or search at YouTube for "net cord tension". See safety information and installation instructions here. (Rev. R4 - 2015, PDF in new window).
1. How was the recommended tension established?
ITF and USTA did studies in the past suggesting that 400-550 pounds tension is an appropriate range for playability. Testing in 3 years of Division 1 men's matches suggests that 400-425 pounds tension is good for the No-Let rule. Testing at the ATP World Tour event in Atlanta, L:A, Cincinnati, and the US Open suggests that the hard-hitting pros like the net cord reaction at a slightly higher tension. See #12 below for discussion about using Singles Sticks.
The only alternate procedure without a net tension device like the TNT Gauge: 1) Release the center strap from the anchor; 2) Crank the net center up to 39" (no longer 40"); and 3) Reconnect the center strap at 36". This procedure is NOT accurate, and USTA and ASBA acknowledge that variables like the net post stiffness and weight of the net can contribute to nets that are much too tight with the "pull-down" procedure.
We do not suggest using tension settings above 475 pounds, due to increased potential for net post and foundation damage.
2. How accurate is the TNT Gauge?
The TNT Gauge contains a specially-designed, corrosion-resistant compression spring with a linear spring rate. The spring manufacturer certifies +/- 5%, but the prototypes have been checked by a certified scales company in Lenoir City, TN to better than 1% accuracy against the indicated force, at 0, 200, 300, and 500 pounds. A copy of the certification is available upon request.
3. How repeatable is the TNT Gauge?
The gauge has been shown to return accurately to its indicated net cord tension after more than 50 cycles up to the Safe Stop (a hard limit at 560 pounds), and return to 0 when removed from the net post. Time-on-net has no effect on the TNT Gauge, which can hold the tension indefinitely.
4. What is the Safe Stop and its function?
The patented Safe Stop is NOT designed to prevent damage to the post and foundation. It is the upper, hard stop limit of the TNT Gauge, preventing the internal spring from seeing more than a measured compression. The benefit to players is a softer impact if they run into the cord (the cord will "give" slightly, then return to the set tension when released, as demonstrated in the video).
5. How does the Safe Stop benefit the net posts and foundations?
The real benefit to the post-foundation system is indicating a playable tension, without over-tightening the net. Our studies show that a typical pair of posts deflects like a leaf spring as much as 7/16" EACH toward the middle at 500 pounds tension. Different post brands exhibit different deflections. For intermittent play, the net cord may be loosened, then returned to the same tension the next time the court is used, reducing the effects of long-term static loading on the foundation. The makers of the TNT Gauge do not claim, suggest, nor imply that addition of the device is intended to prevent damage to the post system.
6. What net posts will the TNT Gauge NOT work with?
There are only a few, older net post brands that are not compatible with the standard TNT Gauge. From the point of hooking the TNT Gauge's lower loop to a post hook or cleat, it needs 14" (Edwards, Cissel/Wilson, and newer Lee/Har-Tru posts) or 11" (Douglas posts) clear on posts plus the length of the existing net cord loop and crimp from the post cap's groove or pulley. We do not recommend use with Elite (Canada) posts, due to the square edge on the cap. It has worked with all posts having two hooks, by attaching to the lower of the two. For posts with internal anchor hooks, please see FAQ #13.
7. What if I have a "caddy" or score stand on the net post?
The net cord must be free to move under the caddy or scoring stand, and the attaching hardware must not interfere with the mounting or range of motion of the cable, its loop, or the TNT Gauge's upper Quick Link. On posts with a single "cleat" anchor, we suggest moving the caddy to a position just below the cleat, where it is functional but out of the way.
8. Is it difficult to install the TNT Gauge?
The short answer: It's easy. One person can install the TNT Gauge in less than five minutes each. For a well-laced net, no help is needed, as the lacing supports the net while the cord is loose. During the NCAA's in Knoxville, two people removed 6 TNT Gauges from the well-laced indoor courts, and reinstalled and calibrated them outdoors in 30 minutes total.
For a loosely laced net, having an assistant to hold up the sagging net while loose is helpful (the net alone puts about 50-75 pounds of tension on the cord); you might find it helpful when installing alone to use a brace about 34" tall under the net cord near the center strap. Yes... you do have to walk the 42 feet from one post to the other two or three times during a solo installation -- once to loosen the net cord, then return to tighten it up to the target tension. Please see Installation Instructions Rev. 4 (2015), here.
9. Why do we need to know the net cord tension?
As noted in several publications (for example, see the section "Net Tension Topic of Study by USTA Tech Group" by Peggy Beard, in the February 22, 2010 issue of Racquet Sports Industry magazine, a net cord that is too soft will "bloop" the ball back to the hitter, or drop it softly over the net when the ball strikes the top of the cord. Conversely, a cord that is too tight will send the ball high in the air, and possibly past the service line or baseline too often.
10. How has net cord tension been set in the past?
The only common method has been to loosen the center strap from its court anchor point, crank the free net up to 40" above the court, then pull the net center down with the center strap. This only implies an unknown tension, and doesn't take into account the variable springiness of the different posts, or weight of the different brands of nets. American Sportsbuilders Association's Tennis Court Construction Manual (p. 129, 2010-2011 edition) suggests this method can easily over-tension a net cord, leading to post and foundation damage.
NOTE: an often-asked question is the effect the TNT Gauge has on the height at the center of the net. Unlike another method recently in development, the TNT Gauge is entirely independent of the net's center strap and has no effect on its setting.
11. Is the net cord "spongy" with the TNT Gauge in place?
No. The net posts still supply the most of the springiness when the net is impacted. The mass of the net, cable, and posts comes into play, in addition to the short throw of the TNT Gauge. The cable takeup from 400 pounds to 500 pounds, for example is only 2/10". The net does not feel soft.
12. Does addition of the singles sticks affect the tension, requiring re-adjustment?
No. Adding or removing the singles sticks shows a tension change of only about 5 pounds (basically the "just noticeable difference" on the indicator scale). This is because the sticks take up a slight amount of cable but that seems to be offset by the additional support that removes part of the weight of the net from the sum of the forces.
July '11 update: Further study from data collected at the Atlanta Tennis Championships is showing that although the net cord tension isn't affected by the addition of singles sticks, there is a significant difference in the playability of the net due to the new net inter-support distance of 34 feet vs. 42 feet without the sticks. Please see the recommended net cord tensions, at the top of this page.
13. My net posts have internal hooks on the anchor post (inside the pipe, no hooks on the outside). Will the TNT Gauge work on my nets?
We can assist you with changing the post's top cap to a grooved version that will take the cable and eye outside the post, then the bolt-on TNT Gauge will act as both the tension indicator and net cable anchor. At retail level, there is no added cost to include the new post cap.
14. My anchor post has an external hook, but a grooved cap instead of a pulley. Will that affect the accuracy?
If the post cap has a groove for the cable, we learned that the vinyl coating on the net cable creates high static friction at higher tensions. Adding a short piece of self-adhesive UHMW Polyethylene tape (revised Jan. 2, 2012 from the original Teflon pipe thread tape for better durability) into the groove at TNT Gauge installation is required for full function. This fixes the sticking, and seems to last indefinitely. This step is described in the installation instructions.
15. Will the TNT Gauge work on outdoor courts, and how durable are they?
April 2014 update: TNT Gauges have been in continuous outdoor use for 3 full years at University of Tennessee, and two years at other facilities including the US Open and University of Georgia. They look almost new, and performance is unaffected.
Feb. 2012: After observing light galvanic corrosion on the plated cables after eight months in the Tennessee weather, all TNT Gauge Pro Systems produced after January 2012 will have stainless steel cables and assembly hardware, especially useful in coastal climates. As of August 1, there is no detectable effect on the cables. And we have had a LOT of rain.
The TNT Gauge's components are selected for weather-resistance, and the design drains rain water well. Examples: The compression spring is chrome-silicon, powder coated; the housing and end blocks are anodized aluminum alloy; the cables and hardware are stainless steel, the indicator is bearing-grade plastic; the label has a permanent adhesive and UV lamination for fade resistance. We are continuing life-expectancy tests now, with no detrimental results so far after 3 years. You can expect the TNT Gauge to survive indefinitely indoors, and greater than 3 years continuously outdoors.
16. How strong is the TNT Gauge, and what happens if it breaks? [Updated June 9, 2011]
The TNT Gauge completed its qualification test series June 9 with destructive testing of two production units. Using the maximum suggested net tension of 550 pounds as a baseline, the TNT Gauge shows a safety margin of 3X in static loading and 3.5X in dynamic loading that simulates a person running into the net with full weight. The full Test Report is here. See a summary on the June 9 News and Updates.
The static failure was very benign, with the Quick Link failing open as intended but remaining attached. Dynamic testing on two units pulled the top loop's cable free, abruptly dropping the housing and fully contained internal components to the base without incident.
Is the TNT Gauge protected intellectual property?
The TNT Gauge is protected by US Patents 8,806,952 and 7,823,466. All the labeling and written content is c2011-2014, by David Glass.
The names TNT Gauge and TNT Gauge Pro, and phrases "Tennis Net Tension Gauge", "Bring Fairness to the Court" are trademarks.