# O vs FCM IoT

The clearest difference is update cadence: FCM IoT at every 3 weeks against O's every 3 months. FCM IoT also leads on iOS requirement (15.0 vs 26.0). 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, FCM IoT every 3 weeks. Both last shipped on October 30, 2026.

## The numbers

| Metric | O | FCM IoT |
| --- | --- | --- |
| 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 3 weeks** |
| Monetization | Free | — |
| Size | 35 MB | 96 MB |
| Requires iOS | 26.0 | **15.0** |
| Devices | iPhone, iPad | **iPhone, iPad, iPod** |
| Age rating | 4+ | 4+ |
| Developer | [Trelleborg Sealing Solutions](https://appshunter.io/developer/396863758) | [苏州曼捷科智能科技有限公司](https://appshunter.io/developer/1530505401) |

## What reviewers say

### O

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

This app helps users calculate O-ring dimensions and find suitable O-ring sizes based on installation specifications. It supports metric and inch measurements and offers chemical compatibility checks for various media.

**Highlights:** O-Ring housing calculation, O-Ring size recommendation, Quick search by international standards, Tolerance calculation, Metric and inch unit switching, Chemical compatibility check

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

**In-app purchases:** none


### FCM IoT

[App page](https://appshunter.io/ios/app/fcm-iot/id1584102216)

**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 FCM IoT free?

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

### Do O or FCM IoT have ads?

Neither O nor FCM IoT shows ads.

### Which is updated more often, O or FCM IoT?

O ships an update every 3 months, and FCM IoT every 3 weeks. Most recently, O was updated on October 30, 2026 and FCM IoT on October 30, 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.*