My kid lost that small base piece to his "20" Thruster Dirt DS Boys' Mountain Bike" Will this work as a replacement?

It depends on the size of the steer tube and stem sizes. I'd the bike has a one inch threaded steer tube it'll work. But, you may have to get a new stem with a 1 1/8 inch collar.

how many spacers could be fit under this adapter?

You don't use spacers for this. You only use spacers for a real threadless setup. This just emulates a threadless and allows you to use a 1-1/8 stem. You just set the height you want and tighten the allen bolt

what stem size does it fit? 1" or 1 1/8"

1 1/8".It inserts into forks with 1 1/8" threaded headsets (actual diameter measurement is 1"). It fits 1 1/8" threadless stems (1 1/8" actual measurement).

How high can you raise the stem above the headset?

I have lifted my stem by 25mm from the top of the threaded steerer into which the extender inserts. Done roughly 2500km, including a 500km bike tour over gravel terrain - no issues whatsoever.

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Profile Design Threadless Size Converter (1" - 1 1/8")

Product ID: 288708444

✨Polished silver finish for sleek aesthetics

📏Approx. 25mm rise increase with spacers

🔩Precision fit for 1" to 1-1/8" steerer conversion

HK$474

Duties & taxes included

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Sold byAmazon Hong KongDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

Buyer Protection · Full refund if your order doesn't arrive as described.

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Description

🚴‍♂️ Elevate your ride with precision and style!

LIGHTWEIGHT DURABLE - Crafted from premium materials to keep your bike agile without added bulk.
SLEEK POLISHED FINISH - Stand out with a high-gloss silver look that complements any bike style.
BOOST YOUR RIDE HEIGHT - Gain up to 25mm rise for enhanced comfort and control using spacers.
SEAMLESS COMPATIBILITY - Effortlessly upgrade your bike with a perfect 1" to 1-1/8" threadless stem fit.
UNIVERSAL FIT FOR ALL RIDERS - Designed unisex and compatible with most quill steerers for versatile use.

The Profile Design Threadless Size Converter transforms a 1" quill steerer to fit a 1-1/8" threadless stem, featuring a polished silver finish and enabling up to 25mm rise increase with spacers. Lightweight and universally compatible, it’s the perfect upgrade for cyclists seeking enhanced fit and sleek aesthetics.

Specifications

ASIN	B0028N14GQ
Batteries Included?	No
Best Sellers Rank	#117,169 in Sporting Goods ( See Top 100 in Sporting Goods ) #137 in Bike Stems
Brand	Profile Design
Color	silber
Customer Reviews	4.5 4.5 out of 5 stars (1,231)
Date First Available	1 January 2024
Department	Unisex
Hand Orientation	Right
Height	1 inches
Included Components	Stems & Converters
Is Discontinued By Manufacturer	No
Item model number	ACTHRCONKT18
Language	English
Length	8 inches
Manufacturer	Profile Design
Material Type	Plastic
Number of Items	1
Product Dimensions	14.61 x 3.18 x 3.81 cm; 113.4 g
Shape	Round
Size	One Size
Sport	Cycling
Usage	Bicycle
Width	3.25 inches

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Our prices include the product cost, international shipping, import duties, customs clearance, and local delivery charges. We handle all customs and import procedures, ensuring there are no hidden fees upon delivery. PRO members receive additional benefits including free shipping.

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TrustScore 4.5 | 7,300+ reviews

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The product exactly matches the description. Very satisfied with my purchase.

5 days ago

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Great price for an authentic product. Fast international shipping too!

3 weeks ago

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HK$474

Duties & taxes included

In stock

Sold byAmazon Hong KongDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

Buyer Protection · Full refund if your order doesn't arrive as described.

Desertcart purchases this item on your behalf and handles shipping, customs, and support to Hong Kong.

Secure transaction

Trustpilot

TrustScore 4.5 | 7,300+ reviews

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The MOLLE sheath is of exceptional quality. Very happy with my purchase.

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Fast shipping and excellent packaging. The Leatherman tool feels very premium and sturdy.

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