# O vs K9 Smart Rings

The clearest difference is update cadence: K9 Smart Rings at every 4 days against O's every 3 months. O's advantage is iOS requirement (12.1 vs 15.1). On price, ads, in-app purchases and device support there is nothing between them.

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

O ships an update every 3 months, K9 Smart Rings every 4 days. The most recent releases landed on October 23, 2026 and October 7, 2026 respectively.

## The numbers

| Metric | O | K9 Smart Rings |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[3.8 (5 ratings)](https://appshunter.io/ios/app/o-ring/id485346224/reviews)** | — |
| Number of ratings | **5** | — |
| Positive reviews | 83.3% of reviews | — |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 3 months | **Every 4 days** |
| Monetization | Free | — |
| Size | 26 MB | 35 MB |
| Requires iOS | **12.1** | 15.1 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 12+ | 4+ |
| Developer | [Trelleborg Sealing Solutions](https://appshunter.io/developer/396863758) | [Simon Prins ACT](https://appshunter.io/developer/1891966426) |

## What reviewers say

### O

[App page](https://appshunter.io/ios/app/o-ring/id485346224)

This app helps users calculate O-Ring dimensions and find compatible materials for their applications. It provides recommendations based on ISO standards and supports both metric and inch measurements.

**Highlights:** O-Ring housing calculation, O-Ring size recommendations by ISO standard, Quick search by national/international standards, O-Ring tolerance calculation, Metric and inch unit switching, Chemical compatibility check, Integration of Trelleborg Sealing Solutions Videos

**Features:** macOS Compatibility

**In-app purchases:** none


### K9 Smart Rings

[App page](https://appshunter.io/ios/app/k9-smart-rings/id6762005957)

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

**In-app purchases:** none


## Frequently asked questions

### Is O free?

O is free to download, with no in-app purchases.

### Is K9 Smart Rings free?

K9 Smart Rings is free to download, with no in-app purchases.

### Do O or K9 Smart Rings have ads?

Neither O nor K9 Smart Rings shows ads.

### Which is updated more often, O or K9 Smart Rings?

O ships an update every 3 months, and K9 Smart Rings every 4 days. Most recently, O was updated on October 23, 2026 and K9 Smart Rings on October 7, 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.*