What goes wrong, and why
| Bar is | What happens | Source |
|---|---|---|
| The wrong shape | It deforms the rivet head | Handbook p. 4-36 |
| Too light | Not enough bucking weight; the material may bulge toward the shop head | Handbook p. 4-36 |
| Too heavy | Its weight and the bucking force may bulge the material away from the shop head | Handbook p. 4-36 |
| Not square to the shank | The shank bends with the first blows and the material is marred with the last | Handbook p. 4-36 |
| Rough or sharp-edged | It marks the surrounding material; faces must be smooth and edges slightly rounded | Handbook p. 4-36 |
How to choose
Shape comes from the job. The bar has to reach the shank end and sit square to it. That is why bars come as sets of odd shapes rather than one block, and why the Handbook names shape before weight.
Weight has a range, not a table. The Handbook gives bars from "a few ounces to 8 or 10 pounds, depending upon the nature of the work", and describes the two failures in the table above. It gives no pounds-per-diameter chart, and neither does AC 43.13-1B. Charts that circulate online are shop practice; this site does not cite them as data.
Let the bar do the work. "Allow the weight of the bucking bar to do most of the work and do not bear down too heavily on the shank." The hands guide and supply rebound. A bar chosen too light invites pushing, which is the wrong fix.
Material. The Handbook describes bars of case-hardened low-carbon steel or alloy bar stock, with faces hard enough to resist denting but not hard enough to shatter.
Bars with published figures
| Bar | Material | Weight | Dimensions | Where |
|---|---|---|---|---|
| Pattern 634 | Cast iron | 0.9 lb | not listed | US · Yardstore |
| 71086 | Cast iron | 1.4 lb | not listed | US · Yardstore |
| Pattern 690 | Cast iron | 2.36 lb | not listed | US · Yardstore |
| ABCD set (4 bars) | Cast iron | not listed | not listed | US · Yardstore |
| Tungsten 74101 | 90+% tungsten | 1.07 lb | not listed | US · Yardstore |
| Tungsten 74211 | 90+% tungsten | 2.4 lb | 0.75 × 1.06 × 8" | US · Yardstore |
| ATS 140 | Cast steel | 2 lb | 5-1/8 × 3 × 1-5/8" | UK/EU · LAS |
| ATS 141 | Cast steel | 3 lb | 10-3/8 × 1 × 2" | UK/EU · LAS |
| ATS 147 | Cast steel | 1.5 lb | 5-1/4 × 2 × 1" | UK/EU · LAS |
| ATS6001 tungsten | Tungsten alloy | not listed | 4 × 1 × 5/8" | UK/EU · LAS |
As the sellers list them. Most US listings give weight without dimensions, and the LAS tungsten listing gives dimensions without weight: ask for the missing figure before buying a bar for a specific reach.
Is tungsten worth it?
Tungsten buys weight in a small bar. LAS describes its tungsten alloy bars as almost twice as heavy as steel for the size, made for "a small yet heavy" bar where a steel one heavy enough would not fit. Yardstore's 2.4 lb tungsten bar measures 0.75" × 1.06" × 8".
So the case is access, not strength: a confined space where the right weight in steel is physically too big. In open structure a steel bar of the right shape and weight does the same job. Price is the other side of the decision: the product pages link to each seller's live listing.
Yardstore's tungsten listings claim reduced vibration and cite a university study without naming it. The Handbook says only that reduced-vibration guns and bars "have been developed to reduce the incidence of carpal tunnel syndrome". We have not found the study, so the claim is reported, not endorsed.
Questions people actually ask
What weight bucking bar for a 1/8 rivet?
Neither the FAA Airframe Handbook nor AC 43.13-1B gives a weight per rivet diameter. The Handbook gives the test instead: too light and the sheet bulges toward the shop head, too heavy and it bulges away. Start with a general-purpose bar and read the rivet.
What is the first thing to look at in a bucking bar?
Shape. The Handbook: "When selecting a bucking bar, the first consideration is shape. If the bar does not have the correct shape, it deforms the rivet head."
Are tungsten bucking bars worth it?
Where space is tight, yes: tungsten gives the needed weight in a bar small enough to fit. In open structure a steel bar of the right shape and weight does the same work.
How many bucking bars do I need?
Commercial kits answer with four: Yardstore's Red Box II and Pro kits ship the same four-bar ABCD set, and its smaller Red Box "737" two of them. Shape variety matters more than count.
Limits of this guide
What the sources support, and no further.
- No weight chart. The primary sources do not publish one, so none is given here.
- No bar was tested. Face finish and balance are not in a listing.
- Listings are incomplete. Weight without dimensions, or the reverse, is common; the table says which is missing.
- Health claims are the sellers'. Vibration figures for tungsten bars are reported as claims.
Sources
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 4 — p. 4-36, "Bucking Bar": shape first, the effects of a bar too light or too heavy, weights from a few ounces to 8 or 10 pounds, holding the bar square; p. 4-39 on reduced-vibration tooling.
- Seller listings — weights and dimensions in the second table, via the linked product pages at Yardstore and LAS Aerospace.