# DuctChecker vs Bolt Length

The clearest difference is price: Bolt Length at Free against DuctChecker's $6.99. Bolt Length also leads on review sentiment (33% vs 0%). DuctChecker's advantage is in-app purchases (none vs 1) and ads (none vs shown). On device support and iOS requirement there is nothing between them.

Bolt Length is free to download; DuctChecker costs $6.99 up front. Bolt Length sells 1 one-off in-app purchase. DuctChecker asks for nothing beyond the download.

DuctChecker ships an update every 4 months, Bolt Length every 20 months. The most recent releases landed on September 7, 2026 and August 2, 2026 respectively.

## The numbers

| Metric | DuctChecker | Bolt Length |
| --- | --- | --- |
| Price | $6.99 | **Free** |
| Rating | — | **[3.0 (2 ratings)](https://appshunter.io/ios/app/bolt-length-nominal-length/id1042345193/reviews)** |
| Number of ratings | — | **2** |
| Positive reviews | 0.0% of reviews | **33.3% of reviews** |
| In-app purchases | **No** | Yes |
| Ads | **No** | Yes |
| Update frequency | **Every 4 months** | Every 20 months |
| Monetization | Paid | **Free with in-app purchases** |
| Size | 23 MB | 6 MB |
| Requires iOS | 15.0 | **14.0** |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [AIR DESIGN, INC.](https://appshunter.io/developer/923430781) | [mitsunori oishi](https://appshunter.io/developer/905649994) |

## What reviewers say

### DuctChecker

[App page](https://appshunter.io/ios/app/ductchecker/id933593987)

Easily calculate duct dimensions using various engineering methods like constant pressure, static pressure regain, total pressure, and velocity. This tool simplifies complex duct design calculations, typically found in flow diagrams or slide rules.

**Highlights:** Constant pressure method calculation, Static pressure regain method, Total pressure method, Velocity method, Duct dimension determination, Simplified duct design

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### Bolt Length

[App page](https://appshunter.io/ios/app/bolt-length-nominal-length/id1042345193)

This application helps calculate the length of metric coarse screws based on Japanese Industrial Standards. It is designed for mechanical design purposes and should be used at the user's own risk.

**Highlights:** Metric coarse screw length calculation, Conforms to Japanese Industrial Standards (JIS), Designed for mechanical design, User risk disclaimer

**Features:** macOS Compatibility, Family Sharing

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Hide Ads | $1.99 | one-time |


## Frequently asked questions

### Is DuctChecker free?

DuctChecker costs $6.99, with no in-app purchases.

### Is Bolt Length free?

Bolt Length is free to download, with in-app purchases available.

### Do DuctChecker or Bolt Length have ads?

Bolt Length shows ads; DuctChecker does not.

### Which is updated more often, DuctChecker or Bolt Length?

DuctChecker ships an update every 4 months, and Bolt Length every 20 months. Most recently, DuctChecker was updated on September 7, 2026 and Bolt Length on August 2, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*