I'm looking to buy a compression tester kit and am a little puzzled by the purpose of the two rubber-ended attachments shown below.
Am I right in assuming that these two attachments can be jammed into the spark plug hole without threading to perform a compression test? If so, wouldn't it blow out due to pressure build-up inside the cylinder?
The product description says:
This item is perfect for checking compression on petrol engine quickly and accurately. It diagnoses problems quickly with 2 rubber cones ends which do not need to thread into head. Our item is suitable for petrol engines on lawn mowers, motorbikes, cars, trucks and so on.